Basri's Lieutenant + Odric's Outrider + Altar of Dementia

Basri's Lieutenant

Odric's Outrider

Altar of Dementia

How it works

1. Activate Altar of Dementia by sacrificing a creature with a +1/+1 counter on it.
2. The creature dies, triggering Basri's Lieutenant and Odric's Outrider.
3. Resolve the Basri's Lieutenant trigger, creating a 2/2 Knight creature token.
4. Resolve the Odric's Outrider trigger, putting a +1/+1 counter on another creature you control.
5. Resolve the Altar of Dementia ability from step 1, causing target player to mill cards equal to the sacrificed creature's power.
6. Repeat.