Still don't agree, but I can see your point.  My thought was that the mention of casting was intended to close the loophole of the healer being invisible and healing everyone while being immune to targeting. Using the imp (or the Quasit or the pseudodragon) seems to be a way of getting around that.  As long as the players and the monsters get to do it, all's fair. :D

Another odd and illogical use of invisibly:

It is only on casting a spell or making an attack which is based on attack rolls or grappling.

So something that is not a spell but uses a save says invisible, like a dragon breath from a dragon under invisibility.

Dragon breath also goes right through magic hut as well. 

All abilities that are based on a save but not a spell work. 

Many a group holed up in a tiny hit and laughed thinking themselves untouchable until bad things happen.

Quote from Mindseye >>

Wrong edition.  In 5th, ANY spellcasting breaks invisibility.  

Invisibility

A creature you touch becomes invisible until the spell ends. Anything the target is wearing or carrying is invisible as long as it is on the target's person. The spell ends for a target that attacks or casts a spell.

You want the improved version.

Greater invisibility

You or a creature you touch becomes invisible until the spell ends. Anything the target is wearing or carrying is invisible as long as it is on the target's person.

this is for the spell invisibility. if you read the stat block, the imp doesn't cast the spell, they use a special way of using invisibility. Those rules are for a different thing entirely. The imps invisibility lasts "until it attacks or until its concentration ends". as for if you were to cast a touch spell attack from the imp and whether or not it would turn visible or not: I don't think theres a RAW answer here. it could really go either way. Personally, I would remove their invisibility because you get the advantages of attacking a target while invisible, thats to say that if the imp is invisible when you make a touch attack from it, the attack does have advantage because the imp is invisible. so I would personally say that the invisibility ends after the attack.

Pretty sure it says the spell is cast as though the imp is casting the spell. Casting a spell is considered using your attack action iirc.

Quote from Sirenir >>

Pretty sure it says the spell is cast as though the imp is casting the spell. Casting a spell is considered using your attack action iirc.

 Nope. 5e is very particular about it's language. Casting a spell is actually the "cast a spell" action. It doesn't say anything about the imp casting a spell. If the imp was casting the spell invisibility, then it would have innate spellcasting at-will invisibility. But it doesn't. It has an ability that's similar, but very clearly different.

i'm playing as a tiefling, blood hunter/warlock, i'm trying to figure out which familiar i want though, imp or psuedodragon

I accidentally let a minor NPC imp become part of the main party because my players adopted him. So this'll come in useful!

This is definitely the best option for pact of chain.

One of my DMs is a huge fan of throwing these at us, and as a result I have learned to hate these things with a passion.

Quote from BlackJohn >>

One of my DMs is a huge fan of throwing these at us, and as a result I have learned to hate these things with a passion.

 Yah, they infuriating little critters; especially if the DM uses invisibility for hit-&-fade attacks.

Quote from Thunder5077 >>

Quote from Sirenir >>

Pretty sure it says the spell is cast as though the imp is casting the spell. Casting a spell is considered using your attack action iirc.

 Nope. 5e is very particular about it's language. 

It is not possible for a rule in an RPG to be so explicit as to account for every conceivable application, nor is it reasonable to contend that any application that is not explicitly prohibited is fair game for exploitation. 

Anyone who wishes to use a familiar as some kind of invisible drone to deliver death-by-proxy would hopefully have the wisdom to check themselves against the realty of the situation, attempting to get away with this sparingly at best. Neither players nor DM's will likely be tolerant of this tactic for very long.

Hey, so, the Invisibility Spells are irrelevant here because the Feature expressly says attacks and concentration breaks are all that break Invis. Nothing regarding Spellcasting whatsoever.

Linking Invisibility or Greater Invisibility does not therefore contribute to understanding.

"Its statistics are the same in each form, except for the speed changes noted"

Does that mean that in its raven form it has the stats of an imp but the abilities of a raven, or the stats and abilities of an Imp and it just looks and flies like a raven?

Actually the warlock is still making the attack roll so it wouldn’t break invisibility either

It's also not using the spell invisibility, its using an ability which specifically says in the statblock  "until it attacks, or loses concentration"

As a complete newb DM, my work-around is that as the spell is not being cast by the Imp then it doesn't break it's invisibility, however, if the spell being cast via the Imp creates/gives off any kind of light or sound then this will give away the presence and/or location of the Imp to all within sight/earshot. I would have the light work a bit like Faerie Fire in that the Imp is highlighted or illuminated and gets no benefits of it's invisibility but just until the end of the round. This would also mean that the Imp's position is known until it moves again. So if the round within which the Imp has been illuminated has finished, but it hasn't moved since then, then I would say that they could be attacked with disadvantage.  

but it literally the, "cast a spell action", how much more explicit does it need to get? 

i almost died to this now my teammate has it enslave 

You and I know very different ravens

/j

Quote from Mindseye >>

Still don't agree, but I can see your point.  My thought was that the mention of casting was intended to close the loophole of the healer being invisible and healing everyone while being immune to targeting. Using the imp (or the Quasit or the pseudodragon) seems to be a way of getting around that.  As long as the players and the monsters get to do it, all's fair. :D

 

 The healer here is the warlock, who is visible. Their spellcasting wasn't hidden, and most intelligent creatures would be able to tell the warlock cast a spell. The warlock is nearly as vulnerable as they would be if they cast the spell normally. The warlock can still be targeting, counterspelled, or even killed. The downside here is both the warlock and the imp had to use their action to cast ONE spell. Is the imp still invisible, yes. But it might not make much of a difference.