Prototype Portal + Dross Scorpion + Phyrexian Altar + Cathodion

Prototype Portal

Dross Scorpion

Phyrexian Altar

Cathodion

How it works

1. Activate Prototype Portal by paying 3 and tapping it, creating a token copy of Cathodion.
2. Activate Phyrexian Altar by sacrificing Cathodion, adding one mana of any color.
3. When Cathodion dies, it and Dross Scorpion trigger.
4. Resolve the Cathodion trigger, adding CCC.
5. Resolve the Dross Scorpion trigger, untapping Prototype Portal.
6. Repeat.