Prototype Portal + Dross Scorpion + Sarcatog + Myr Moonvessel

Prototype Portal

Dross Scorpion

Sarcatog

Myr Moonvessel

How it works

1. Activate Prototype Portal by paying 1 and tapping it, creating a token copy of Myr Moonvessel.
2. Activate Sarcatog 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 Sarcatog ability, giving it +1/+1 until end of turn.
7. Repeat.