Tatterkite + Dross Scorpion + Cauldron of Souls + Phyrexian Altar

Tatterkite

Dross Scorpion

Cauldron of Souls

Phyrexian Altar

How it works

1. Activate Cauldron of Souls by tapping it, giving Tatterkite persist until end of turn.
2. Activate Phyrexian Altar by sacrificing Tatterkite, adding one mana of any color.
3. Tatterkite dies, triggering its persist ability and Dross Scorpion.
4. Resolve the Tatterkite trigger, returning it from your graveyard to the battlefield with no -1/-1 counters on it.
5. Resolve the Dross Scorpion trigger, untapping Cauldron of Souls.
6. Repeat.