Mikaeus, the Unhallowed + Ashnod's Altar + Safehold Elite

Mikaeus, the Unhallowed

Ashnod's Altar

Safehold Elite

How it works

1. Activate Ashnod's Altar by sacrificing Safehold Elite.
2. When Safehold Elite dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
3. Activate Ashnod's Altar by sacrificing Safehold Elite.
4. When Safehold Elite dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
5. Repeat.