I have a question regarding familiars and area spells. More specifically, Sleep.
I have a player that wanted to cast this spell around a given target, that he could only see from his familiar's eyes (not from himself). We allowed the effect at the time to maintain the session, but now looking at the rules…
We are looking at page 204 of the book and to me it seems this is not possible. Does the effect originates from his body, or from the familiar when he is using its eyes?
However, the point the player raises (that that same paragraph can be interpreted as being able to see the target, which he can due to the familiar; plus the fact that you can case a touch spell from 100ft… makes me think that you should in fact be able to cast such a spell from the familiar.
Confused!
In any case, this question is just to find out… per the raw, if it is possible or not. If yes, all good. If not, then we learn and make a feat for him to be able to do it.
Feel free to advise if you would advise against allowing this with a custom feat. I cannot see any issues with it.
Best Answer
Your player's familiar cannot cast Sleep for them. Familiars can only deliver touch-ranged spells.
Sleep has a range of 90'; the caster picks a target within 90' which will be the origin of what follows. Find Familiar specifies that a when you cast a spell with range of touch the familiar "can deliver the spell as if it had cast the spell." Since Sleep doesn't have a range of touch, the familiar is not the one casting Sleep.
As such, the PC casts Sleep according to the usual targeting rules you've referenced: "you [the caster] must have a clear path to it." The sight granted by the familiar isn't germane as it's not the caster. You need look only at the path from the caster (PC) to the target point.
(Even if the PC could use the familiar's sight as a way to re-figure line-of-sight, @yinzanat rightly reminds us that the action economy imposes a limit. Seeing through the familiar's eyes requires an action, as does also the casting of Sleep.)