Sidisi, Undead Vizier
Legendary Creature — Zombie Snake
Deathtouch
Exploit (When this creature enters the battlefield, you may sacrifice a creature.)
When Sidisi, Undead Vizier exploits a creature, you may search your library for a card, put it into your hand, then shuffle your library.
Illustrated by
Dragons of Tarkir#120RareEnglishLegality
Rulings
A creature with exploit “exploits a creature” when the controller of the exploit ability sacrifices a creature as that ability resolves.
You choose whether to sacrifice a creature and which creature to sacrifice as the exploit ability resolves.
You can sacrifice the creature with exploit if it’s still on the battlefield. This will cause its other ability to trigger.
If the creature with exploit isn’t on the battlefield as the exploit ability resolves, you won’t get any bonus from the creature with exploit, even if you sacrifice a creature. Because the creature with exploit isn’t on the battlefield, its other triggered ability won’t trigger.
You can’t sacrifice more than one creature to any one exploit ability.