Stalwart Successor + Kithkin Spellduster + Yahenni, Undying Partisan

Stalwart Successor

Kithkin Spellduster

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. When Kithkin Spellduster enters, Stalwart Successor triggers, putting a +1/+1 counter on Kithkin Spellduster
4. Resolve the Yahenni ability.
5. Repeat.