Metalwork Colossus + The Ooze + Blasting Station + Gorma, the Gullet

Metalwork Colossus

The Ooze

Blasting Station

Gorma, the Gullet

How it works

1. Cast Metalwork Colossus by paying 0, which enters with at least two +1/+1 counters on it due to Gorma.
2. When Metalwork Colossus enters, Blasting Station triggers, untapping Blasting Station.
3. Activate Blasting Station by tapping it and sacrificing Metalwork Colossus.
4. When Metalwork Colossus dies, Gorma and The Ooze trigger.
5. Resolve The Ooze's trigger, creating a Mutagen token for each +1/+1 counter Metalwork Colossus had.
6. Resolve Gorma's trigger, putting a +1/+1 counter on it.
7. Resolve the Blasting Station ability.
8. Activate Metalwork Colossus by sacrificing two Mutagens, returning it from your graveyard to your hand.
9. Repeat.

This clever engine loops Metalwork Colossus in and out of your graveyard by using its massive mana value to cast it for free, heavily discounted by the noncreature artifacts you control. Each time the Colossus enters, it triggers Blasting Station to untap, allowing you to sacrifice the Colossus right back to Blasting Station's activation to deal damage. When the Colossus dies, Gorma, the Gullet grants a +1/+1 counter while triggering The Ooze to churn out Mutagen tokens based on those counters. You can then cash in two of those very same Mutagen tokens to return the Metalwork Colossus from your graveyard straight back to your hand, ready to cast all over again.