Prototype Portal + Dross Scorpion + Myr Moonvessel + Bloodflow Connoisseur

Prototype Portal

Dross Scorpion

Myr Moonvessel

Bloodflow Connoisseur

How it works

1. Activate Prototype Portal by paying 1 and tapping it, creating a token copy of Myr Moonvessel.
2. Activate Bloodflow Connoisseur 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 Bloodflow Connoisseur ability, putting a +1/+1 counter on it.
7. Repeat.