Prototype Portal + Dross Scorpion + Phyrexian Altar + Myr Moonvessel

Prototype Portal

Dross Scorpion

Phyrexian Altar

Myr Moonvessel

How it works

1. Activate Prototype Portal by paying 1 and tapping it, creating a token copy of Myr Moonvessel.
2. Activate Phyrexian Altar by sacrificing Myr Moonvessel, adding one mana of any color.
3. When Myr Moonvessel dies, it and Dross Scorpion trigger.
4. Resolve the Myr Moonvessel trigger, adding 1.
5. Resolve the Dross Scorpion trigger, untapping Prototype Portal.
6. Repeat.