Koll, the Forgemaster + Deathrender + Altar of Dementia

Koll, the Forgemaster

Deathrender

Altar of Dementia

How it works

1. Activate Altar of Dementia by sacrificing the creature with Deathrender attached.
2. When the creature dies, Koll and Deathrender trigger.
3. Resolve the Koll trigger, returning the creature from your graveyard to your hand.
4. Resolve the Deathrender trigger, putting the creature from your hand onto the battlefield and attaching Deathrender to it.
5. Resolve the Altar of Dementia ability from step 1, causing a player to mill cards equal to the creature's power.
6. Repeat.