Animation Module + Scion of the Swarm + Phyrexian Altar + Dross Harvester

Animation Module

Scion of the Swarm

Phyrexian Altar

Dross Harvester

How it works

1. Activate Phyrexian Altar by sacrificing another creature, adding CC.
2. When the creature dies, Dross Harverster's second ability triggers, causing you to gain 2 life.
3. Scion of the Swarm triggers, putting a +1/+1 counter on itself.
4. Animation Module triggers, causing you to pay 1 to create a 1/1 Servo artifact creature token.
5. Repeat.

This crafty loop is quietly held together by Dross Harvester, whose life-gaining trigger each time a creature dies acts as the vital spark for the entire engine. That life gain immediately prompts Scion of the Swarm to grow with a new +1/+1 counter, which in turn wakes up Animation Module's first ability to generate a fresh Servo artifact creature token for just one mana. Finally, that newly minted token feeds directly into Phyrexian Altar as a sacrifice to fund the process and keep the cycle spinning infinitely.