Prototype Portal + Dross Scorpion + Altar of Dementia + Cathodion

Prototype Portal

Dross Scorpion

Altar of Dementia

Cathodion

How it works

1. Activate Prototype Portal by paying 3 and tapping it, creating a token copy of Cathodion.
2. Activate Altar of Dementia by sacrificing Cathodion.
3. When Cathodion dies, Cathodion and Dross Scorpion trigger.
4. Resolve the Cathodion trigger, adding CCC.
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.