Cauldron of Souls + Dross Scorpion + Grinding Station + Biotransference

Cauldron of Souls

Dross Scorpion

Grinding Station

Biotransference

How it works

1. Activate Cauldron of Souls by tapping it, giving the creature with bloodthirst persist until end of turn.
2. Activate Grinding Station by tapping it and sacrificing the creature with bloodthirst.
3. When the creature dies, its persist ability and Dross Scorpion trigger.
4. Resolve the persist trigger, returning the creature from your graveyard to the battlefield, which enters the battlefield with at least one +1/+1 counter on it due to its bloodthirst ability.
5. When the creature enters the battlefield, Grinding Station triggers, untapping Grinding Station.
6. Resolve the Dross Scorpion trigger, untapping Cauldron of Souls.
7. Resolve the Grinding Station ability from step 2, causing target player to mill three cards.
8. Repeat.