Stalwart Successor + Grazing Kelpie + Phantom Train

Stalwart Successor

Grazing Kelpie

Phantom Train

How it works

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