Improvise (Your artifacts can help cast this spell. Each artifact you tap after you’re done activating mana abilities pays for {1}.)

Search your library for an artifact card with mana value X or less, put it onto the battlefield, then shuffle.

All creatures get -3/-3 until end of turn.

You may cast a spell with mana value 3 or less from your hand without paying its mana cost.

All creatures get -3/-3 until end of turn.

You may cast a spell with mana value 3 or less from your hand without paying its mana cost.

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.

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.