Basri's Lieutenant + Serra Redeemer + Altar of Dementia

Basri's Lieutenant

Serra Redeemer

Altar of Dementia

How it works

1. Activate Altar of Dementia by sacrificing another creature with a +1/+1 counter on it.
2. The creature dies, triggering Basri's Lieutenant's second ability, creating a 2/2 Knight creature token.
3. When the Knight enters the battlefield, Serra Redeemer triggers, putting two +1/+1 counters on the Knight.
4. Resolve the Altar of Dementia ability from step 1, causing target player to mill cards equal to the sacrificed creature's power.
5. Repeat.