Stalwart Successor | Umbral Collar Zealot (and one other card)

Persist Creature

Cards

Activate
Umbral Collar Zealot by sacrificing the creature with persist.
When that creature dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
When that creature enters,
Stalwart Successor triggers, putting a +1/+1 counter on it.
Remove a +1/+1 and a -1/-1 counter from that creature as a state-based action.
Resolve the
Umbral Collar Zealot ability.
Repeat.

This combo has been estimated to be Exhibition (Bracket 1+).