Prototype Portal + Dross Scorpion + Grinding Station + Myr Moonvessel

Prototype Portal

Dross Scorpion

Grinding Station

Myr Moonvessel

How it works

1. Activate Prototype Portal by paying 1 and tapping it, creating a token copy of Myr Moonvessel.
2. When the token Myr Moonvessel enters, Grinding Station triggers, untapping itself.
3. Activate Grinding Station by sacrificing Myr Moonvessel and tapping it.
4. When Myr Moonvessel dies, Myr Moonvessel and Dross Scorpion trigger.
5. Resolve the Myr Moonvessel trigger, adding C.
6. Resolve the Dross Scorpion trigger, untapping Prototype Portal.
7. Resolve the Grinding Station ability, causing target player to mill three cards.
8. Repeat.