Adarkar Valkyrie + Thornbite Staff + Altar of Dementia

Adarkar Valkyrie

Thornbite Staff

Altar of Dementia

How it works

1. Activate Adarkar Valkyrie by tapping it, targeting another nontoken creature you control.
2. Activate Altar of Dementia by sacrificing the creature targeted in step 1.
3. When the creature dies, Adarkar Valkyrie triggers twice.
4. Resolve the first trigger, untapping Adarkar Valkyrie.
5. Resolve the second trigger, returning the sacrificed creature from your graveyard to the battlefield.
6. Resolve the Altar of Dementia ability, causing target player to mill cards equal to the sacrificed creature's power.
7. Repeat.