Mikaeus, the Unhallowed + Thermopod + Grazing Kelpie

Mikaeus, the Unhallowed

Thermopod

Grazing Kelpie

How it works

1. Activate Thermopod 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. Activate Thermopod by sacrificing Grazing Kelpie.
4. When Grazing Kelpie dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
5. Repeat.