Clarification: Fainting Spell

[ChaosJim]

http://pokegym.net/forums/showthread.php?t=88062&highlight=gengar+uxie+fainting+spell


I just read that, I'm still unclear about something:

Will Gengar still flip, attempting to KO my opponent's NEW active Pokemon?

If that Pokemon were Muk for example (Fossil, Toxic Gas) would Gengar not get to flip?

[PokePop]

Gengar only gets to try to KO the Pokemon that KO'd it.
If that Pokemon has left play before the attack ends (as part of an effect from that attack), then there is no Pokemon there to try to KO and so Fainting Spell fails.
One might say that Fainting Spell is still flipped for, but there would be no Pokemon to KO if it flipped heads.