Quote from Rezzahan »You choose what to sacrifice when the trigger resolves. If Ilharg's trigger resolves first and gives you another creature, you can sacrifice that creature to Greven. So all you need to do is stack the triggers correctly.
Quote from FetalTadpole »
You do it during the end step of the player whose turn is before you. They untap on your untap and get sacrificed at the beginning of YOUR end step.
Quote from bobthefunny »Typically a necro this old would get locked - but since this has seen quite a bit of interest and activity, (no doubt due to Anje), I'll leave this conversation to proceed naturally.
Just be aware if quoting someone... they might not be looking for the same answer today... =p
Quote from spezza19 »Necrotic Ooze, Kiki-Jiki, Mirror Breaker is pretty simple. Both good standalone cards, too.