Stalwart Successor + Carrion Feeder + Persistent Constrictor

Stalwart Successor

Carrion Feeder

Persistent Constrictor

How it works

1. Activate Carrion Feeder 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 Carrion Feeder ability.
5. Repeat.

This clever loop relies on the interaction between Carrion Feeder and Persistent Constrictor, where sacrificing the Constrictor sends it to the graveyard only for its persist ability to bring it right back with a -1/+1 counter. That entering-the-battlefield event immediately triggers Stalwart Successor, whose passive ability recognizes the first counters placed on the creature that turn and counters out the persist drawback by adding a +1/+1 counter. Because +1/+1 and -1/+1 counters annihilate each other as a state-based action, the Persistent Constrictor is left entirely clean of counters and ready to be sacrificed to the Feeder all over again.