You are currently under the effects of Invisibility, and then you cast Invisibility or Greater Invisibility on yourself for whatever reason. Do you remain completely invisible throughout the turn or do you "pop" into visibility only to instantly "pop" back out?
"Casting another spell that requires concentration. You lose concentration on a spell if you cast another spell that requires concentration. You can't concentrate on two spells at once."
"Invisbility: The spell ends for a target that attacks or casts a spell."
In my opinion, "casting another spell" and "casts a spell" occurs when the character begins to cast the spell and not only when it completes. The rules don't specify exactly how long a spell takes to cast if its casting time is only one action.
However, for spells requiring more than one action to cast it says "When you cast a spell with a casting time longer than a single action or reaction, you must spend your action each turn casting the spelt, and you must maintain your concentration while you do so"
This would tend to support the idea that concentration on a previous spell ends when you begin to cast the next spell since concentration is required during the casting of at least some spells.
Based on this, I would say the original invisibility flickers out briefly (probably a second or two ... not defined in the rules) as the caster drops concentration before being replaced by the one being cast.
I'm of a mind that there is no discernible flicker.
David42 points out some very good arguments and presents a strong case for the flicker. The reason behind my take on this is the part where he states that casting the spell would take concentration.
If a spell takes concentration to cast then it would negate the idea that you don't break concentration when casting a non-concentration spell.
Normal activity, such as moving and attacking, doesn’t interfere with concentration. The following factors can break concentration:
Casting another spell that requires concentration. You lose concentration on a spell if you cast another spell that requires concentration. You can’t concentrate on two spells at once.
Taking damage. Whenever you take damage while you are concentrating on a spell, you must make a Constitution saving throw to maintain your concentration.
Due to the fact that you can move and attack without interfering with concentration then the act of casting a spell would not affect the Invisibility spell until the casting is complete. Attacks can take the form of melee, range, or spell, so casting Firebolt, using the argument David42 presented, would drop any concentration spell.
I believe that page 5 of xanathar's states that when you begin casting a spell that requires concentration while concentrating on a spell, you lose concentration on the first spell and it's effects that are tied to concentration end. I don't know if there are more than the invisibility spell and the greater invisibility spell, but both of them require concentration so there would be a flicker. If there was an effect that had a creature invisible that didn't require its concentration (ie. Invisibility cast on it by another creature), then there wouldn't be a flicker when the invisible creature cast it as long as there isn't a clause similar to "Invisbility: The spell ends for a target that attacks or casts a spell." I'm guessing that either the invisible condition or the associated spells typically have that clause though.
I guess the answer would then fall to the "ask the DM" if you're playing in a group or determine whether there would be a flicker in your world when you are the DM.
That's a fair point, while I haven't read any of Xanthar's, I can see using that interpretation.
However, for people who only have access to the PHB or basic information from the SRD or Phandelver, does that mean the concentration information is incorrect? Does Xanthar's interpretation over-rule the PHB/SRD?
I'd rule that you would become invisible to the invisibility spell. The new spell would like to make you invisible, but it can't find you, so the new invisibility spell just fails. I made a Protection from Protection spell recently, it's a similar principle :P
The rule from Xanathar's has also appears in the PHB, at least my 1oth printing PHB states that you lose concentration on a spell when you begin casting another spell that requires concentration. Page 203.
If you cast the first invisibility on yourself the spell would end when you began casting the second invisibility. If someone else has cast invisibility on you, you would use the invisibility from the spell you cast following the rule for combining magical effects. In this case you would not lose invisibility, there would be no flicker. If you were invisible due to a magic item there would be a flicker if the invisibility granted by the magic item ends when you cast a spell.
You can freely cast non-concentration spells while continuing concentrating on a single concentration spell, unless the specific spell says otherwise.
That's a fair point, while I haven't read any of Xanthar's, I can see using that interpretation.
However, for people who only have access to the PHB or basic information from the SRD or Phandelver, does that mean the concentration information is incorrect? Does Xanthar's interpretation over-rule the PHB/SRD?
I don't think it's so much that the information is incorrect, but perhaps incomplete. I think Xanathar's is probably a RaW version of the PHB RaI but I don't think it was put in errata. As such, it's definitely in that gray area of DM interpretation more than other things.
Even with the Xanathar ruling, I wouldn't have an issue either way since it's mostly flavor at that point. The flicker could make for some interesting "I need to lay off the liquor/drugs/late nights" type of role play moments for when the guard sees the character flicker and does the double take to discover that they don't see anything.
As the spell casting is one action, and there can be multiple turns with multiple actions within a six-second round, I don't think the flicker would be long. I might even require a perception check for anyone who wasn't looking for it to notice it.
The Xanathar's text is the same as in my PHB, but I would say you can always use the rules you have as the rules for your campaign. The important thing is to have a consistent set of rules that everybody can agree on.
The exact scenario I'm hypothesizing in my head is as follows:
• Creature is wearing Ring of Invisibility • Round 1: Cast Greater Invisibility on Self • Rounds 2-12: (Main Action) Any spells or actions that don't break Concentration • Round 12: (Bonus Action) Reapply Invisibility from the ring
This should lead to no "popping" if I understand the rules as given.
There will be a pop. Ring of Invisibility states that the invisibility will end if the wearer casts a spell. If someone else cast Greater Invisibility on you there would be no pop.
The invisibility will end even if you do not cast a concentration spell immideatly, as spell clearly states that casting a spell breaks the invisibility. Then you will become invisible again at the end of your action. So you are visible through the entire casting process, which is not quantified in the mechanical system of the game, but in theory it's probably less than 2 seconds.(as via race/class features, you can move same distance as your movement, action and bonus action in some races or classes, and a turn means 6 seconds at most usually much less, your casting of one action would probably take at most 2 seconds, probably somewhere around a second(which does not mean anything for mechanics). Anyway you are visible through your action and an npc or player capable of attacking you with his reaction can even attack you in that time(mage slayer?) if he has the prequisite abilities and circumstances(distance)(don't mean to necro, thought this subject might intrigue and confuse some players...)
The invisibility will end even if you do not cast a concentration spell immideatly, as spell clearly states that casting a spell breaks the invisibility.
So if you're invisible, and you cast fire bolt, do you have advantage on the attack roll as an unseen attacker? Because it sounds like some people are saying you become visible as soon as you begin casting the next spell, which means you would be visible when the fire bolt went off. That doesn't sound right to me.
So if you're invisible, and you cast fire bolt, do you have advantage on the attack roll as an unseen attacker? Because it sounds like some people are saying you become visible as soon as you begin casting the next spell, which means you would be visible when the fire bolt went off. That doesn't sound right to me.
Yea I have to agree with Devin here. As long as you aren't concentrating on one of the invisibility spells then casting a spell or attacking would end the invisibility per the description but I have to think that it does so at the end of the action otherwise you wouldn't get the benefit of being unseen when making the attack/spell and that seems very wrong to me.
Of course if you had cast the original Invisibility/Greater Invisibility spell on yourself then you would pop out during the casting of the second one (same as with any other concentration spell) but that's because of the concentration rules, not because of the standard rules for invisibility.
I'm really not a big fan of this answer, but the aforementioned SAC entry seems to make it pretty clear that as soon as you start casting a concentration spell, concentration on the old one ends. This would also apply in a situation where someone is flying by way of the fly spell, and they want to recast it. They are going to fall.
In the case of invisibility, I'm saying they do pop back in for just a moment and then become invisible again. And if you had a readied attack or something that triggered upon seeing the invisible creature, you could make an argument that the creature is visible enough to be a target at that moment.
The invisibility will end even if you do not cast a concentration spell immideatly, as spell clearly states that casting a spell breaks the invisibility.
So if you're invisible, and you cast fire bolt, do you have advantage on the attack roll as an unseen attacker? Because it sounds like some people are saying you become visible as soon as you begin casting the next spell, which means you would be visible when the fire bolt went off. That doesn't sound right to me.
Why would i give advantage, casting negates invisibility(so you are seen) and spell has verbal components effectively causing an initiative roll making your location apparent due to sound even if you are not in line of sight. Though if you used a subtle spell through any character feature and casted the spell without a sound effect i would make it a surprise attack in most cases(assuming the character has no features to negate surprise attacks), also casting the subtle spell from a blindspot of the target should automatically have advantage as he is not aware of it, unseen/unheard advantage works here. Living in a fantasy setting makes everyone a bit paranoid, think of cats, how they react to sound, that is what keeps you alive, in our society its called ADHD but in old societies where law enforcement was weak it was simply like jungle at nights in many places, you had to be vigilant, i think fictional people and creatures in fantasy settings are even more alert.
Shortly, no the instant you cast firebolt you become visible. If you are getting advantage it won't be from being unseen unless you are casting it from a blindspot of the target. You do not just pop, you are visible for the duration of an action, which has no time value given mechanically but it is long enough for you to evoke a word or two, since spell component of the Greater invisiblity spell includes verbal components as well as somatic components, even worse for regular invisiblity as it also have material components, even if you are a dextrous wizard there is a casting process which involves a material, hand gestures holding a gum arabic and incantations, or at least waving of a spell focus in a certain pattern accompanied by incantations. Casting a spell is shiny business in most cases(at least that is how both original D&D and WoTC artists visualized spell casting for decades) o.o
Though we use flanking on our table so, getting advantage for a spell or attack isn't really hard if you can reposition yourself fast. But normal invisiblity is not meant for getting advantage for casters in most cases(though you can use it for scouting or repositioning yourself to a blindspot for getting advantage), unlike greater invisibility(why do you think they have such vast level and duration difference?)...
You can cast spells like catapult(only somatic component and no spell effects stem from you as the point of origin) in greater invisibility/non detection and the target will fail to find you unless he has a non divination spell/natural feature to make him/her/it find you( a spell that grants him such ability, or shapeshifts him to a creature with such ability). Still firebolt will fail while it will get advantage due to being unseen, due to launch point of spell on a grid map, it will decrease the survival chance of the aggresor against smart targets with experience in fighting casters(do not forget this though, many unexperienced NPCs will probably panic, while experienced npcs will quickly deploy tactics, animals will trust their instincts and attack or run away in most cases if their perception fails, DMs need to think in different ways for each kind of npc, their past experiences their intelligence score matters as much as their perception/ as perception is not only seeing, but also hearing and smelling, some spells use spell components that stink, and those mages often carry them in pouches on their belts, you know guano and sulphur have a strong odor and most mages carry them o.o) .
Sometimes i see players taking on adventures/campaigns against enemies with 20+ intelligence, eg: Acererak, when they encounter a spell that does not appear in his readied spells for the day, they start criticising immedeatly in younger parties, thing is many DMs of my generation, change the prepared spells of high level npc casters almost everyday in campaing(and we keep record of it), so if an adventuring group makes their enemy learn their where abouts, plans and strengths, a smart villain, as expected alters his plans accordingly, that is common sense and if that villain has 27 intelligence you are in for probably an impossible mission(that is why i do not understand WoTC for releasing such adventure/campaign, who can win against a demilich with 27 intelligence in a campaign if DM runs the game in a way governed by logic, sorry for going off topic).
Yes, invisibility's intended usage is escaping, ambush and scouting but that does not mean wizard has to these him/herself, when a rogue rolls stealth dice that can be detected by his own passive perception, he will think he is not walking silent enough and would probably reroll in his next action, so cast invisibility/greater invisibility on a rogue who is expert in perception and stealth(also has observant feat perhaps?) he/she will make far better use of it than any other class, or useless familiars.(do not forget to get climbing speed somehow either mariner fighting style, thief subclass or spider climb spell which is also concentration, man this is why we love arcane trickster, more casters the merrier, not really :) we like player characters with no spell casting as DMs :))
"And if you had a readied attack or something that triggered upon seeing the invisible creature, you could make an argument that the creature is visible enough to be a target at that moment"
Yeah actually there won't even be arguement; ready attack, it's triggers and application: Upon seeing an enemy that pops out(be it stealth, blink or invisibility) within my line of sight i will attack or if i hear a sound of incantation(in this case the caster might be behind you) from somewhere out of my line of sight i will turn to the source of sound and attack, i would demand a 15 DC perception check(no check for Passive perception 15, also i wouldn't ask for an action for that check, imho it's a state of being alert) for the latter and that's it. A caster, casting a subtle(silent) spell does not trigger the second condition ofcourse and gets to complete his action unscathed according to trigger conditions above. (If the ready action owner is a beastmaster or familiar owning class with a pet with keen smelling and did not forget to mention it while readying his action, i might even consider applying the advantage to the perception check, as a cat/wolf would probably make certain sounds the caster/ranger is used to, to make the targets location apparent in such cases)
I know some information here is not directly relevant to question asked by the original poster, but for clarity's sake, i gave my two cents about invisibility/invisiblity&sneak counter related gameplay for a wider range of circumstances...
I'm really not a big fan of this answer, but the aforementioned SAC entry seems to make it pretty clear that as soon as you start casting a concentration spell, concentration on the old one ends. This would also apply in a situation where someone is flying by way of the fly spell, and they want to recast it. They are going to fall.
I'd say it's a little more complicated in the case of fly specifically, because that spell states "the target falls if it is still aloft, unless it can stop the fall"; well what is recasting the spell if not stopping the fall? So I'd say that in that case specifically the language allows for recasting without falling.
More generally though, we know that the intention in the rules is that timing is somewhat loose except when the order of events actually matters; for example, if you read the rules as strictly as possible, then the only way to short rest inside a rope trick is to keep the rope short enough to climb in the same round you cast it. But in practice you won't find many DM's who will rule that a short rest has to last for exactly 600 rounds; a couple of rounds lost to climbing in/out is unlikely to matter to them, and the designers have stated this is the intention.
Now on the issue of invisibility and whether you'd "flicker" while recasting; in a combat or stealth situation that would count as one where the timing does matter. Whether or not it has to be a "flicker" is somewhat academic, personally I'd rule that a new Stealth check should be triggered anyway unless you've taken steps to hide the casting (e.g- you used the Subtle Spell Metamagic, or did the casting in a hiding place or such) this will determine whether any nearby creature(s) see a "flicker", or hear a sound or whatever makes sense at the time.
I think the most interesting case is if a creature is invisible as a result of the invisibility spell, and needs to recast it while a nearby creature has chosen to Ready an attack. Since you're ending concentration on the previous spell to start casting the new one, and because a reaction interrupts the current creature's turn, there is effectively a window during which the creature is visible for at least as long as it takes to resolve the attack. If you want to be a super strict DM you could roll that readied attack without disadvantage, but personally due to the tight (and vague) timing I'd probably either impose disadvantage anyway (due to the difficulty of the shot) or roll some kind of check to see if the creature spots an early sign of the first spell fading, such that they can fire as their target becomes visible.
As others have said though, for any effect that doesn't require concentration, you essentially have two sources of the invisible condition, so you have it no matter what, though you may still need to roll for Stealth depending upon how the new effect is triggered (e.g- a vocal component).
You are currently under the effects of Invisibility, and then you cast Invisibility or Greater Invisibility on yourself for whatever reason. Do you remain completely invisible throughout the turn or do you "pop" into visibility only to instantly "pop" back out?
"Casting another spell that requires concentration. You lose concentration on a spell if you cast another spell that requires concentration. You can't concentrate on two spells at once."
"Invisbility: The spell ends for a target that attacks or casts a spell."
In my opinion, "casting another spell" and "casts a spell" occurs when the character begins to cast the spell and not only when it completes. The rules don't specify exactly how long a spell takes to cast if its casting time is only one action.
However, for spells requiring more than one action to cast it says "When you cast a spell with a casting time longer than a single action or reaction, you must spend your action each turn casting the spelt, and you must maintain your concentration while you do so"
This would tend to support the idea that concentration on a previous spell ends when you begin to cast the next spell since concentration is required during the casting of at least some spells.
Based on this, I would say the original invisibility flickers out briefly (probably a second or two ... not defined in the rules) as the caster drops concentration before being replaced by the one being cast.
I'm of a mind that there is no discernible flicker.
David42 points out some very good arguments and presents a strong case for the flicker. The reason behind my take on this is the part where he states that casting the spell would take concentration.
If a spell takes concentration to cast then it would negate the idea that you don't break concentration when casting a non-concentration spell.
Due to the fact that you can move and attack without interfering with concentration then the act of casting a spell would not affect the Invisibility spell until the casting is complete. Attacks can take the form of melee, range, or spell, so casting Firebolt, using the argument David42 presented, would drop any concentration spell.
I believe that page 5 of xanathar's states that when you begin casting a spell that requires concentration while concentrating on a spell, you lose concentration on the first spell and it's effects that are tied to concentration end. I don't know if there are more than the invisibility spell and the greater invisibility spell, but both of them require concentration so there would be a flicker. If there was an effect that had a creature invisible that didn't require its concentration (ie. Invisibility cast on it by another creature), then there wouldn't be a flicker when the invisible creature cast it as long as there isn't a clause similar to "Invisbility: The spell ends for a target that attacks or casts a spell." I'm guessing that either the invisible condition or the associated spells typically have that clause though.
I guess the answer would then fall to the "ask the DM" if you're playing in a group or determine whether there would be a flicker in your world when you are the DM.
That's a fair point, while I haven't read any of Xanthar's, I can see using that interpretation.
However, for people who only have access to the PHB or basic information from the SRD or Phandelver, does that mean the concentration information is incorrect? Does Xanthar's interpretation over-rule the PHB/SRD?
I'd rule that you would become invisible to the invisibility spell. The new spell would like to make you invisible, but it can't find you, so the new invisibility spell just fails. I made a Protection from Protection spell recently, it's a similar principle :P
Looking for new subclasses, spells, magic items, feats, and races? Opinions welcome :)
The rule from Xanathar's has also appears in the PHB, at least my 1oth printing PHB states that you lose concentration on a spell when you begin casting another spell that requires concentration. Page 203.
If you cast the first invisibility on yourself the spell would end when you began casting the second invisibility. If someone else has cast invisibility on you, you would use the invisibility from the spell you cast following the rule for combining magical effects. In this case you would not lose invisibility, there would be no flicker. If you were invisible due to a magic item there would be a flicker if the invisibility granted by the magic item ends when you cast a spell.
You can freely cast non-concentration spells while continuing concentrating on a single concentration spell, unless the specific spell says otherwise.
I don't think it's so much that the information is incorrect, but perhaps incomplete. I think Xanathar's is probably a RaW version of the PHB RaI but I don't think it was put in errata. As such, it's definitely in that gray area of DM interpretation more than other things.
Even with the Xanathar ruling, I wouldn't have an issue either way since it's mostly flavor at that point. The flicker could make for some interesting "I need to lay off the liquor/drugs/late nights" type of role play moments for when the guard sees the character flicker and does the double take to discover that they don't see anything.
As the spell casting is one action, and there can be multiple turns with multiple actions within a six-second round, I don't think the flicker would be long. I might even require a perception check for anyone who wasn't looking for it to notice it.
The Xanathar's text is the same as in my PHB, but I would say you can always use the rules you have as the rules for your campaign. The important thing is to have a consistent set of rules that everybody can agree on.
This has given me a lot of food for thought.
The exact scenario I'm hypothesizing in my head is as follows:
• Creature is wearing Ring of Invisibility
• Round 1: Cast Greater Invisibility on Self
• Rounds 2-12: (Main Action) Any spells or actions that don't break Concentration
• Round 12: (Bonus Action) Reapply Invisibility from the ring
This should lead to no "popping" if I understand the rules as given.
There will be a pop. Ring of Invisibility states that the invisibility will end if the wearer casts a spell. If someone else cast Greater Invisibility on you there would be no pop.
The invisibility will end even if you do not cast a concentration spell immideatly, as spell clearly states that casting a spell breaks the invisibility. Then you will become invisible again at the end of your action. So you are visible through the entire casting process, which is not quantified in the mechanical system of the game, but in theory it's probably less than 2 seconds.(as via race/class features, you can move same distance as your movement, action and bonus action in some races or classes, and a turn means 6 seconds at most usually much less, your casting of one action would probably take at most 2 seconds, probably somewhere around a second(which does not mean anything for mechanics). Anyway you are visible through your action and an npc or player capable of attacking you with his reaction can even attack you in that time(mage slayer?) if he has the prequisite abilities and circumstances(distance)(don't mean to necro, thought this subject might intrigue and confuse some players...)
As a DM I would house rule that you never become visible.
But it is a house rule in my opinion.
So if you're invisible, and you cast fire bolt, do you have advantage on the attack roll as an unseen attacker? Because it sounds like some people are saying you become visible as soon as you begin casting the next spell, which means you would be visible when the fire bolt went off. That doesn't sound right to me.
"Not all those who wander are lost"
Read the Invisibility and greater invisibility descriptions.
Yea I have to agree with Devin here. As long as you aren't concentrating on one of the invisibility spells then casting a spell or attacking would end the invisibility per the description but I have to think that it does so at the end of the action otherwise you wouldn't get the benefit of being unseen when making the attack/spell and that seems very wrong to me.
Of course if you had cast the original Invisibility/Greater Invisibility spell on yourself then you would pop out during the casting of the second one (same as with any other concentration spell) but that's because of the concentration rules, not because of the standard rules for invisibility.
I'm really not a big fan of this answer, but the aforementioned SAC entry seems to make it pretty clear that as soon as you start casting a concentration spell, concentration on the old one ends. This would also apply in a situation where someone is flying by way of the fly spell, and they want to recast it. They are going to fall.
In the case of invisibility, I'm saying they do pop back in for just a moment and then become invisible again. And if you had a readied attack or something that triggered upon seeing the invisible creature, you could make an argument that the creature is visible enough to be a target at that moment.
"Not all those who wander are lost"
Why would i give advantage, casting negates invisibility(so you are seen) and spell has verbal components effectively causing an initiative roll making your location apparent due to sound even if you are not in line of sight. Though if you used a subtle spell through any character feature and casted the spell without a sound effect i would make it a surprise attack in most cases(assuming the character has no features to negate surprise attacks), also casting the subtle spell from a blindspot of the target should automatically have advantage as he is not aware of it, unseen/unheard advantage works here. Living in a fantasy setting makes everyone a bit paranoid, think of cats, how they react to sound, that is what keeps you alive, in our society its called ADHD but in old societies where law enforcement was weak it was simply like jungle at nights in many places, you had to be vigilant, i think fictional people and creatures in fantasy settings are even more alert.
Shortly, no the instant you cast firebolt you become visible. If you are getting advantage it won't be from being unseen unless you are casting it from a blindspot of the target. You do not just pop, you are visible for the duration of an action, which has no time value given mechanically but it is long enough for you to evoke a word or two, since spell component of the Greater invisiblity spell includes verbal components as well as somatic components, even worse for regular invisiblity as it also have material components, even if you are a dextrous wizard there is a casting process which involves a material, hand gestures holding a gum arabic and incantations, or at least waving of a spell focus in a certain pattern accompanied by incantations. Casting a spell is shiny business in most cases(at least that is how both original D&D and WoTC artists visualized spell casting for decades) o.o
Though we use flanking on our table so, getting advantage for a spell or attack isn't really hard if you can reposition yourself fast. But normal invisiblity is not meant for getting advantage for casters in most cases(though you can use it for scouting or repositioning yourself to a blindspot for getting advantage), unlike greater invisibility(why do you think they have such vast level and duration difference?)...
You can cast spells like catapult(only somatic component and no spell effects stem from you as the point of origin) in greater invisibility/non detection and the target will fail to find you unless he has a non divination spell/natural feature to make him/her/it find you( a spell that grants him such ability, or shapeshifts him to a creature with such ability). Still firebolt will fail while it will get advantage due to being unseen, due to launch point of spell on a grid map, it will decrease the survival chance of the aggresor against smart targets with experience in fighting casters(do not forget this though, many unexperienced NPCs will probably panic, while experienced npcs will quickly deploy tactics, animals will trust their instincts and attack or run away in most cases if their perception fails, DMs need to think in different ways for each kind of npc, their past experiences their intelligence score matters as much as their perception/ as perception is not only seeing, but also hearing and smelling, some spells use spell components that stink, and those mages often carry them in pouches on their belts, you know guano and sulphur have a strong odor and most mages carry them o.o) .
Sometimes i see players taking on adventures/campaigns against enemies with 20+ intelligence, eg: Acererak, when they encounter a spell that does not appear in his readied spells for the day, they start criticising immedeatly in younger parties, thing is many DMs of my generation, change the prepared spells of high level npc casters almost everyday in campaing(and we keep record of it), so if an adventuring group makes their enemy learn their where abouts, plans and strengths, a smart villain, as expected alters his plans accordingly, that is common sense and if that villain has 27 intelligence you are in for probably an impossible mission(that is why i do not understand WoTC for releasing such adventure/campaign, who can win against a demilich with 27 intelligence in a campaign if DM runs the game in a way governed by logic, sorry for going off topic).
Yes, invisibility's intended usage is escaping, ambush and scouting but that does not mean wizard has to these him/herself, when a rogue rolls stealth dice that can be detected by his own passive perception, he will think he is not walking silent enough and would probably reroll in his next action, so cast invisibility/greater invisibility on a rogue who is expert in perception and stealth(also has observant feat perhaps?) he/she will make far better use of it than any other class, or useless familiars.(do not forget to get climbing speed somehow either mariner fighting style, thief subclass or spider climb spell which is also concentration, man this is why we love arcane trickster, more casters the merrier, not really :) we like player characters with no spell casting as DMs :))
"And if you had a readied attack or something that triggered upon seeing the invisible creature, you could make an argument that the creature is visible enough to be a target at that moment"
Yeah actually there won't even be arguement; ready attack, it's triggers and application: Upon seeing an enemy that pops out(be it stealth, blink or invisibility) within my line of sight i will attack or if i hear a sound of incantation(in this case the caster might be behind you) from somewhere out of my line of sight i will turn to the source of sound and attack, i would demand a 15 DC perception check(no check for Passive perception 15, also i wouldn't ask for an action for that check, imho it's a state of being alert) for the latter and that's it. A caster, casting a subtle(silent) spell does not trigger the second condition ofcourse and gets to complete his action unscathed according to trigger conditions above. (If the ready action owner is a beastmaster or familiar owning class with a pet with keen smelling and did not forget to mention it while readying his action, i might even consider applying the advantage to the perception check, as a cat/wolf would probably make certain sounds the caster/ranger is used to, to make the targets location apparent in such cases)
I know some information here is not directly relevant to question asked by the original poster, but for clarity's sake, i gave my two cents about invisibility/invisiblity&sneak counter related gameplay for a wider range of circumstances...
I'd say it's a little more complicated in the case of fly specifically, because that spell states "the target falls if it is still aloft, unless it can stop the fall"; well what is recasting the spell if not stopping the fall? So I'd say that in that case specifically the language allows for recasting without falling.
More generally though, we know that the intention in the rules is that timing is somewhat loose except when the order of events actually matters; for example, if you read the rules as strictly as possible, then the only way to short rest inside a rope trick is to keep the rope short enough to climb in the same round you cast it. But in practice you won't find many DM's who will rule that a short rest has to last for exactly 600 rounds; a couple of rounds lost to climbing in/out is unlikely to matter to them, and the designers have stated this is the intention.
Now on the issue of invisibility and whether you'd "flicker" while recasting; in a combat or stealth situation that would count as one where the timing does matter. Whether or not it has to be a "flicker" is somewhat academic, personally I'd rule that a new Stealth check should be triggered anyway unless you've taken steps to hide the casting (e.g- you used the Subtle Spell Metamagic, or did the casting in a hiding place or such) this will determine whether any nearby creature(s) see a "flicker", or hear a sound or whatever makes sense at the time.
I think the most interesting case is if a creature is invisible as a result of the invisibility spell, and needs to recast it while a nearby creature has chosen to Ready an attack. Since you're ending concentration on the previous spell to start casting the new one, and because a reaction interrupts the current creature's turn, there is effectively a window during which the creature is visible for at least as long as it takes to resolve the attack. If you want to be a super strict DM you could roll that readied attack without disadvantage, but personally due to the tight (and vague) timing I'd probably either impose disadvantage anyway (due to the difficulty of the shot) or roll some kind of check to see if the creature spots an early sign of the first spell fading, such that they can fire as their target becomes visible.
As others have said though, for any effect that doesn't require concentration, you essentially have two sources of the invisible condition, so you have it no matter what, though you may still need to roll for Stealth depending upon how the new effect is triggered (e.g- a vocal component).
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You "pop" in and then back out since your concentration ends immediately when you start casting another concentration spell