Stalwart Successor + Ashnod's Altar + Grazing Kelpie

Stalwart Successor

Ashnod's Altar

Grazing Kelpie

How it works

1. Activate Ashnod's Altar 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. Repeat.