[quote=@vancexentan]
It's Red not black but that point is irrelevant.

I don't especially like poison stuff so I'm going to let Turbo get the first word in. From what i see this could be troublesome to balance in some cases, especially in buildings, and melee servants are pretty much unable to go directly for her if they know about the second noble phantasm because then they are stick in essentially a giant poison bubble. Any masters who aren't directly powerful who get stuck in it are even worse off. But Noble phantasms are meant to be power so once again I'll leave turbo to this one.
[/quote]

It's not that different from Jack's Mist, so it should be fine. Might be prudent to add something about how magi can use the principles of Resistance to last marginally longer inside the poison compared to normal people, but otherwise I don't see much of a problem with it. Servants wouldn't have much of a problem escaping from buildings anyway, given most of them can punch down walls with their bare hands.