Gerrard, Weatherlight Hero + Cauldron of Souls + Extruder + Altar of Dementia

Gerrard, Weatherlight Hero

Cauldron of Souls

Extruder

Altar of Dementia

How it works

1. Activate Cauldron of Souls by tapping it, giving Gerrard persist until end of turn.
2. Activate Extruder by sacrificing Cauldron of Souls, putting a +1/+1 counter on Gerrard.
3. Activate Altar of Dementia by sacrificing Gerrard.
4. When Gerrard dies, it and its persist ability trigger.
5. Resolve the Gerrard persist trigger, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
6. Resolve the second Gerrard trigger, failing to exile it as it has left your graveyard, and returning Cauldron of Souls from your graveyard to the battlefield.
7. Resolve the Altar of Dementia ability from step 3, causing target player to mill cards equal to Gerrard's power.
8. Repeat.