Prototype Portal + Dross Scorpion + Altar of Dementia + Myr Moonvessel

Prototype Portal

Dross Scorpion

Altar of Dementia

Myr Moonvessel

How it works

1. Activate Prototype Portal by paying 1 and tapping it, creating a token copy of Myr Moonvessel.
2. Activate Altar of Dementia 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 Altar of Dementia ability, milling target player a number of cards equal to the sacrificed creature's power.
7. Repeat.