Metalwork Colossus + The Ooze + Yahenni, Undying Partisan + Bioengineered Future

Metalwork Colossus

The Ooze

Yahenni, Undying Partisan

Bioengineered Future

How it works

1. Cast Metalwork Colossus by paying 0, which enters with at least two +1/+1 counters on it due to Bioengineered Future.
2. Activate Yahenni 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 Yahenni ability.
5. Activate Metalwork Colossus by sacrificing two Mutagens, returning it from your graveyard to your hand.
6. Repeat.