Altar of Dementia + Thran Vigil + Grazing Kelpie

Altar of Dementia

Thran Vigil

Grazing Kelpie

How it works

1. Activate Altar of Dementia 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. Thran Vigil triggers, putting a +1/+1 counter on Grazing Kelpie.
4. Resolve the Altar of Dementia ability.
5. Repeat.