Umbral Collar Zealot + Thran Vigil + Persistent Constrictor

Umbral Collar Zealot

Thran Vigil

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. Thran Vigil triggers, putting a +1/+1 counter on Persistent Constrictor.
4. Resolve the Umbral Collar Zealot ability.
5. Repeat.

This clever loop relies on Umbral Collar Zealot as the sac outlet that constantly bins Persistent Constrictor, whose own persist ability naturally brings it back to the battlefield with a -1/-1 counter. Because Persistent Constrictor is an artifact creature leaving the graveyard during your turn, Thran Vigil sees it depart and immediately places a +1/+1 counter on it, which neatly cancels out the newly applied -1/-1 counter through state-based actions. This leaves Persistent Constrictor pristine and ready to be sacrificed all over again, generating endless death triggers, sacrifice triggers, and repeatable surveil.