Kithkin Spellduster + Thran Vigil + Yahenni, Undying Partisan

Kithkin Spellduster

Thran Vigil

Yahenni, Undying Partisan

How it works

1. Activate Yahenni by sacrificing Kithkin Spellduster.
2. When Kithkin Spellduster dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
3. Thran Vigil triggers, putting a +1/+1 counter on Kithkin Spellduster.
4. Resolve the Yahenni ability.
5. Repeat.