Prototype Portal + Dross Scorpion + Grinding Station + Cathodion

Prototype Portal

Dross Scorpion

Grinding Station

Cathodion

How it works

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