Prototype Portal + Dross Scorpion + Extruder + Myr Moonvessel

Prototype Portal

Dross Scorpion

Extruder

Myr Moonvessel

How it works

1. Activate Prototype Portal by paying 1 and tapping it, creating a token copy of Myr Moonvessel.
2. Activate Extruder by sacrificing Myr Moonvessel.
3. When Myr Moonvessel dies, Myr Moonvessel and Dross Scorpion trigger.
4. Resolve the Myr Moonvessel trigger, adding C.
5. Resolve the Dross Scorpion trigger, untapping Prototype Portal.
6. Resolve the Extruder ability, putting a +1/+1 counter on it.
7. Repeat.