Metalwork Colossus + The Ooze + Altar of Dementia + Bloodspore Thrinax

Metalwork Colossus

The Ooze

Altar of Dementia

Bloodspore Thrinax

How it works

1. Cast Metalwork Colossus by paying 0, which enters with at least two +1/+1 counters on it due to Bloodspore Thrinax.
2. Activate Altar of Dementia by sacrificing Metalwork Colossus.
3. When Metalwork Colossus dies, The Ooze triggers, creating a Mutagen token for each +1/+1 counter Metalwork Colossus had.
4. Resolve the Altar of Dementia ability.
5. Activate Metalwork Colossus by sacrificing two Mutagens, returning it from your graveyard to your hand.
6. Repeat.