Stalwart Successor + Umbral Collar Zealot + Persistent Constrictor

Stalwart Successor

Umbral Collar Zealot

Persistent Constrictor

How it works

1. Activate Umbral Collar Zealot by sacrificing Persistent Constrictor
2. When Persistent Constrictor dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
3. When Persistent Constrictor enters, Stalwart Successor triggers, putting a +1/+1 counter on Persistent Constrictor
4. Resolve the Umbral Collar Zealot ability.
5. Repeat.