Sigil Captain + Rosie Cotton of South Lane + Crystalline Crawler + Ooze Flux + Pir, Imaginative Rascal

Sigil Captain

Rosie Cotton of South Lane

Crystalline Crawler

Ooze Flux

Pir, Imaginative Rascal

How it works

1. Activate Ooze Flux by paying 1 and removing a +1/+1 counter from a creature you control, creating a 1/1 Ooze creature token.
2. Rosie Cotton of South Lane triggers, putting two +1/+1 counters on Crystalline Crawler due to Pir.
3. When the Ooze enters the battlefield, Sigil Captain triggers, putting four +1/+1 counters on it due to Pir.
4. Activate Crystalline Crawler's first ability twice by removing two +1/+1 counters from it, adding 1.
5. Repeat.
6. Once you have infinite Oozes with a +1/+1 counter on them, you may remove those counters to create an infinitely large Ooze using Ooze Flux.