Altar of Dementia + Wingrattle Scarecrow + Thran Vigil

Altar of Dementia

Wingrattle Scarecrow

Thran Vigil

How it works

1. Activate Altar of Dementia by sacrificing Wingrattle Scarecrow.
2. When Wingrattle Scarecrow 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 Wingrattle Scarecrow.
4. Resolve the Altar of Dementia ability.
5. Repeat.

This fascinating loop lets you continuously mill your opponents by feeding Wingrattle Scarecrow to Altar of Dementia, turning the sacrifice and subsequent return into an engine for infinite death triggers and self-mill. The trick only works because of Thran Vigil, whose passive ability capitalizes on the scarecrow leaving your graveyard by placing a +1/+1 counter on it every time it returns. That +1/+1 counter immediately neutralizes the -1/+1 counter placed by the persist ability, resetting the scarecrow so it can be sacrificed all over again.