My group is about to face an enemy who can turn invisible. The first thing they are talking about, of course, is for the wizard to learn see invisibility. I have thoughts on how to run this, but figured I would get some opinions and advise. See invisibility can only be cast on self and;

For the duration, you see invisible creatures and objects as if they were visible, and you can see into the Ethereal Plane. Ethereal creatures and objects appear ghostly and translucent.

For the wizard, I can see him being able to attack normally (without disadvantage), however, I do not see this giving anyone else in the group the same, unless the wizard uses his action as a help action to point out the creature to another pc. At least this is how I was going to play it. Thoughts?

I can also see my group trying to throw something like flour to make the creature visible...how would you run that? I am inclined not to allow it, but do not know exactly how to explain it. 

I think once the wizard throws any kind of attack roll (not AOE) at the guy, the other characters will know to attack the same spot, at least until the monster's turn, and can attack with disadvantage, but cannot cast spells that require sight of the target. I also think if the wizard wants to point, that shouldn't cost an action, just a free action, but the other character must succeed on a Perception check to correctly guess the exact square where he's pointing. Failure on the Perception check means they will attack empty space. If they're relying on pointing, they might be better off using AOE spells, since in that case they might only have to guess approximately, and the Perception check DC will be lower (maybe 0 if the monster is close).

"For the wizard, I can see him being able to attack normally (without disadvantage), however, I do not see this giving anyone else in the group the same, unless the wizard uses his action as a help action to point out the creature to another pc. At least this is how I was going to play it. Thoughts?"

I would run it as you suggests. The wizard using his Helpaction, to cancel out the disadvantage for other attacking Player. But he just can do that for one player. As a free action he can tell the other mombers the position of the Enemy, so that they can attack the right square, where the enemie's at. Otherwise they wouldn't notice where the enemy is standing and have to attack on suggestions.

"I can also see my group trying to throw something like flour to make the creature visible...how would you run that? I am inclined not to allow it, but do not know exactly how to explain it."

A lot of people think, this is a bad idea.  
Reason: It's magic. Countering magic with flour seems a little strange. 

I however, think this is great, but it doesnt work as the you would think. Because evey flour that connects with the Body of the invisible creature will get invisible too. So a creature can use it's action to cover 1 5-foot square with flour. The creature wil be "visible" for 1 round, if it fails a dex save to avoid the flour, because you will see the silhuette in the falling flour fo a short time. After the round the flour has fallen to the ground, and everything that touched the Creature will be invisible.

The DC should be relative low, because flour is not as effective as you would suggest, to make invisible creatures visible. 

I’m pretty sure the correct ruling is actually as soon as an invisible creature attacks, everyone knows where it is: in fact, unless the invisible creature is actively sneaking, everyone knows where it is. They have disadvantage and it has advantage because they can’t see it, but they know its general area enough to attack. (If it’s not engaged with anyone, I would allow it to take the Hide action to resume stealth until it attacks again, though.) And Ron is right on about the flour becoming invisible.

Just remember, it’s better to err on the side of weak when ruling invisibility, because if it’s strong your party wizard can and will use it against you later!

Flour thrown at the invisible critter won't make the critter itself visible, but it will make their footprints clearly visible.  Passive perception should easily pick that up until the critter leaves the square it is in.  Even then, some might be tracked along behind the caster for another 5 feet or so.

There are no Free Actions in 5th Edition D&D as such.  That was a thing in previous Editions.  As of now, there are a great many things you can do freely, but not as an Action.  You can move for free, you can talk, almost all you like, and you can mess with Objects.  You could almost certainly point a finger, say "There!", and remove all Disadvantage.

Quote from Geann >>

You could almost certainly point a finger, say "There!", and remove all Disadvantage.

I don't think that would remove disadvantage. "There!" would, on a grid, point you to the grid square. But a creature could be anywhere inside its grid square, unless you're talking very large ones. "There!" would allow you to know the right square to shoot at, or swing at, and would allow you to attack the individual at all. Otherwise, if the invisible creature is moving, you won't even know what square to attack (always, of course, depending on circumstance). Notice the rules even imply this -- the creature's location can be detected if it moves/makes noise/etc., but the 2nd bullet, attack rolls against it have Disadvantage, is not written as being conditional upon the first bullet. It doesn't say "unless its location is given way by making noise or leaving tracks, attack rolls have disadvantage." it says "it may give itself away" separate from "attack rolls are made at disadvantage."

The way I run this (and we just had this happen last session) -- if you have some way of knowing the grid square the target is in (moving, tracks, in this case ripples in the water), you can attack the proper grid square with disadvantage. If you have no way of knowing the grid square in which the creature resides, then you have to declare what square you are attacking, and the attack is made with disadvantage from the player's end, but from the GM's end, if it's the wrong grid square, it's an auto-miss. Depending on circumstances, I may describe that they can tell it's the wrong square or not.

If you see someone hit the target, you know the grid square the target was in at the moment of that attack, so you can probably target the right square. If someone points it out to you, same thing.

If they fail the roll, no amount of "It's right there!", by the other players will do any good in finding it.

RAW or no RAW, I would not rule that way. I would rule that "It's right there!" points it out enough that other PCs could attack with disadvantage. Again, using grid squares simply for the ease of explanation, "It's right there" tells you what grid square they are in. But I recognize that this is how *I* would rule and is not necessarily RAW. I'm perfectly willing to rule against RAW when I think RAW (or RAI) doesn't make any logical sense. And to me "it's right there!" doesn't do you any good -- makes no logical sense.

In a large area, especially if players are spread out, "it's right there" could be any number of grid points, as players don't share the same line of sight, hence different perspectives

We use a VTT and I use walls and terrain walls to represent line of sight. If a PC does not have line of sight when the person says "He's right there!" that PC would not be able to see what was pointed out. In fact, this exact circumstance happened last session, and one of the party members didn't see what was pointed out, and could not attack at that point. She had to move to a better vantage point.

How would you adjudicate a situation where the players are in an area, say 100 x 100, and spread out in a line some 40 feet across, the BBEG is some 80 feet away from the Wizard, where the Wizard is at one end of the line?

As a matter of convenience, in our game, I allow all players to point out specific grid squares to each other. Yes, I know that in character, the farther away this is, due to parallax etc., the harder it would be to locate the specific grid square or hex, but going all the way back to the 1980s and Champions, we have always allowed each other to point out specific squares or hexes as targets. Also, in the dark, a BBEG who is 80' away would be in a square that is not visible to most of the players, and in the VTT, they wouldn't be able to see it even if someone used the X key in the interface to manifest a colored hand and point it out (which Foundry lets us do). This has happened to me a few times as GM when I have tried to point something out with the X-hand and one of the players says, "We can't see that." Since as GM, I can see the whole map, I sometimes don't realize what they can/can't see.

Actually a lot of this is solved by the VTT. I can make the token vanish, for example, so they actually can't see where the guy is. Then they have to X-hand what grid square they are attacking and hope it's right. Etc. The invisibility played quite well in the session last week, IMO.

My feeling is this. "He's Right There!" pointing out a 5' x 5' grid square is still pointing out an area 25 square feet in area (or 125 cubic feet in volume for 3D). That's a general enough area that it's not specific, but allows an attack into that hex or square, at Disadvantage. A hit means you get lucky.

BTW, a few of my players, who are quite smart, had an inspiration saved up, and at several points used their inspiration to negate the disadvantage and get the hit. IMO, this is smart play, and I not only had no problem with it but thought it was a perfect use of inspiration.

Everyone know where an invisible creature is, unless it's also hidden. Those that can see invisible creature will attack it normally but otherwise have no way to help others that cannot see invisible in order to get around it. 

 I'd rule that flour would remove the possibility for the invisible creature to make stealth check due as of being invisible but otherwise woiuld remain invisible as you still dont see it, you only see flour that is on it.

The way most Virtual Table handle things that you can't see via Fog of War or Dynamic Lighting runs contrary to how D&D 5E rules handle it. In 5E, you know where all combattants are, unless they are hidden. Being blinded, invisible, in darkness or out of line of sight in the upcoming corridor should not mask creatures position in an encounter.

There are some other spells available that might help depending on what other classes are in the party.

Faerie Fire for one.

This is one of those situations where the players need to be specific about what it is they are doing. If the guy goes invisible and moves and the player just says "I attack him" They would be attacking where he was, and not where he is, and thusly not be able to hit the invisible individual no matter how hard they try. If the Wizard with See Invisibility were to point out where the invisible creature was, then the group would be able to make attack rolls with disadvantage against the creature assuming the wizard is able to adequately describe where the invisible person is.

This is ignoring any additional ways of perceiving the creature, like trying to locate it by means other than sight, like hearing or smell both of which are viable alternatives. There are also complications with magical effects that can reveal the location of the creature (IE faerie fire as mentioned above), area of effect things, or direction of attack (with bows/guns and other ranged attack methods like the catapult spell) that would, in theory, hit anything in the line that it was fired from and not the specific space. 

This is overcomplicating the issue.

In combat unless the enemy took the Hide action you still know where it is and can target with any anything that doesn't require seeing them - which includes attacks. The difference are the advantages and disadvantages the invisible condition imposes. See Invisibility means the wizard can ignore those - the enemy is not invisible for the wizard, and therefore the enemy can't really benefit from taking a Hide action since it can be seen. 

And that's it.

Anything more than the above, which is the RAW, is added homebrewing tomfoolery that is not necessary and a headache. 

I stumbled on a Q&A from the Devs saying RAW See Invisibility doesn't counter the Invisible condition's 2nd bullet, and therefore attack rolls against the invisible creature have disadvantage, and the creature’s attack rolls have advantage. Where one affected by Faerie Fire specifically can’t benefit from being Invisible.

Ask The Sage | D&D Celebration 2021 (20:40)

Yeah, I'll be ruling different. 

See Invisibility specifically says "as if it were visible". Not "as if it were partially visible" like his predator-cloaking analogy. 

His explanation reeks of "we ****ed up but let's pretend this was intentional". 

I prefer to rely on Unseen Attackers and Targets rule for this. ☺

I assume invisibility is just restating unseen attackers and targets, but the entire way the vision rules are written up is a disaster.