Find Familiar- who casts the touch spell?

[diplomancer]

Here's the relevant text from Find Familiar (emphasis added)

Finally, when you Cast a Spell with a range of touch, your familiar can deliver the spell as if it had cast the spell. Your familiar must be within 100 feet of you, and it must use its Reaction to deliver the spell when you cast it. If the spell requires an Attack roll, you use your Attack modifier for the roll.

I never thought too much about that clause. At least not until I started playing a Pact of the Chain Warlock, with a Sprite as my favourite familiar. Here's what the statblock says:

The sprite magically turns Invisible until it attacks or casts a spell

Now, if that means the sprite loses invisibility when you use that Find Familiar feature (and notice Sprites don't cast spells from their stat block), it means it's casting the spell, right?

And so, the next question, with deep balance issues involved, is: who's concentrating on that spell?

Please discuss.

[Amnestic]

With regards to Concentration, you do, not your familiar:

and it must use its Reaction to deliver the spell when you cast it

With regards to breaking invisibility, by the same logic it wouldn't break unless delivering the spell involved an attack roll. I think. Maybe. It would still break it from being Hidden though.

[Contrast]

RAW I think its pretty clear that the caster both cast and concentrates on the spell.

I think there's definitely an argument both ways about if the sprite would remain invisible in the case of a non-attack touch spell however for what its worth I think I would probably rule that it would break the sprites invisibility (because that feels right to me rather than any specific rules text).

[No brains]

One possible hitch here is that 'cast' has two definitions in regards to spells in 5e, as we see in the description for Glyph of Warding.

...Spell Glyph: You can store a prepared spell of 3rd Level or lower in the glyph by casting it as part of creating the glyph. The spell must target a single creature or an area. The spell being stored has no immediate Effect when cast in this way. When the glyph is triggered, the stored spell is cast...

Unfortunately, it's possible to read this passage as 'cast' meaning both the actions taken in order to release the spell and the release of the spell itself. While that's not normally a problem, it can create confusion in situations like Find Familiar when one creature takes the actions to release a spell while another creature is the physical conduit of its release.

Of course, I think it would be reasonable either way for a DM to decide if a familiar counts as casting a spell for the purposes of breaking invisibility, but it really ought to be discussed and then kept consistent.

[PhantomSoul]

RAW I think its pretty clear that the caster both cast and concentrates on the spell.

Agreed; the Find Familiar effect is that the Familiar

can deliver the spell as if it had cast the spell

(emphasis mine)... it doesn't do everything like it cast the spell, and specifically it doesn't cast the spell like it cast the spell nor does it concentrate like it cast the spell because it doesn't cast the spell (only delivers the spell like it cast the spell).

[diplomancer]

Agreed; the Find Familiar effect is that the Familiar (emphasis mine)... it doesn't do everything like it cast the spell, and specifically it doesn't cast the spell like it cast the spell nor does it concentrate like it cast the spell because it doesn't cast the spell (only delivers the spell like it cast the spell).

As I see it: either the Sprite's not casting the spell, and thus does not lose invisibility (unless it's a touch attack spell, in which case he loses his invisibility for making an attack, not for casting the spell), or, if he loses the invisibility just for casting the spell, he has cast the spell, and so's the one concentrating on it.

I believe the first interpretation both makes more sense and is more balanced; this is more of a warning to DMs about the consequences of ruling that the sprite loses invisibility.

[dafrca]

This has never come up on my table, but if it did, I woudl go with the Caster is casting the spell and is the one to maintain the concentration and the Sprite does not lose invisibility because they didn't cast a spell.

This feels like it is right to me.