Koll, the Forgemaster + Phyrexian Altar + Obsidian Battle-Axe + Grim Initiate

Koll, the Forgemaster

Phyrexian Altar

Obsidian Battle-Axe

Grim Initiate

How it works

1. Cast Grim Initiate by paying .
2. Grim Initiate enters the battlefield, triggering Obsidian Battle-Axe, attaching it to Grim Initiate.
3. Activate Phyrexian Altar by sacrificing Grim Initiate, adding .
4. Grim Initiate dies, triggering itself and Koll.
5. Resolve Grim Initiate's trigger, amassing 1.
6. Resolve Koll's trigger, returning Grim Initiate from your graveyard to your hand.
7. Activate Phyrexian Altar by sacrificing the Zombie Army token, adding one mana of any color.
8. Repeat.
9. Once you have infinite mana, you may repeat the loop without sacrificing the Zombie Army token.