Nim Deathmantle + Cathodion + Phyrexian Altar

Nim Deathmantle

Cathodion

Phyrexian Altar

How it works

1. Activate Phyrexian Altar by sacrificing Cathodion, adding one mana of any color.
2. Cathodion and Nim Deathmantle trigger.
3. Resolve the Cathodion trigger, adding CCC.
4. Resolve the Nim Deathmantle trigger, causing you to pay 4 to return Cathodion from your graveyard to the battlefield, and then attach Nim Deathmantle to it.
5. Repeat.