Cauldron of Souls + Dross Scorpion + Phyrexian Altar + Biotransference

Cauldron of Souls

Dross Scorpion

Phyrexian Altar

Biotransference

How it works

1. Activate Cauldron of Souls by tapping it, giving the creature with bloodthirst persist until end of turn.
2. Activate Phyrexian Altar by sacrificing the creature with bloodthirst, adding one mana of any color.
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. Resolve the Dross Scorpion trigger, untapping Cauldron of Souls.
6. Repeat.