Stalwart Successor + Lesser Masticore + Phantom Train

Stalwart Successor

Lesser Masticore

Phantom Train

How it works

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