Shuffle your library, then exile the top four cards. You may cast any number of spells with mana value 5 or less from among them without paying their mana costs. Lands you control don't untap during your next untap step.

Target creature gains undying until end of turn. (When it dies, if it had no +1/+1 counters on it, return it to the battlefield under its owner's control with a +1/+1 counter on it.)

Until end of turn, target creature gains "When this creature dies, return it to the battlefield tapped under its owner's control with a +1/+1 counter on it."

Haste

Whenever a creature an opponent controls dies, put a +1/+1 counter on Yahenni, Undying Partisan.

Sacrifice another creature: Yahenni gains indestructible until end of turn.