Mikaeus, the Unhallowed + Plague Belcher + Yahenni, Undying Partisan

Mikaeus, the Unhallowed

Plague Belcher

Yahenni, Undying Partisan

How it works

1. Activate Yahenni by sacrificing Plague Belcher.
2. When Plague Belcher dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
3. When Plague Belcher enters the battlefield, it triggers, putting a -1/-1 counter on it.
4. Resolve the Yahenni ability
5. Repeat.