Stalwart Successor + Phantom Train + Persistent Constrictor

Stalwart Successor

Phantom Train

Persistent Constrictor

How it works

1. Activate Phantom Train 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 Phantom Train ability.
5. Repeat.

This clever loop revolves around Phantom Train's ability to consume your own board state as fuel, sacrificing Persistent Constrictor to grow itself. Thanks to persist, Persistent Constrictor immediately returns from the graveyard with a -1/-1 counter, which in turn satisfies Stalwart Successor's trigger condition for placing the first counters on a creature that turn. Stalwart Successor steps in to place a +1/+1 counter on Persistent Constrictor, which immediately annihilates the -1/-1 counter through state-based actions and leaves the snake clean and ready to be sacrificed all over again.