You have at least one +1/+1 counter on a creature you control.
Mana Needed
({1} magic symbol) ({G} magic symbol) available.
Steps
Activate
Ooze Flux by paying ({1} magic symbol) ({G} magic symbol) and removing a +1/+1 counter from a creature you control, creating a 1/1 Ooze creature token.
Rosie Cotton of South Lane triggers, putting two +1/+1 counters on
Crystalline Crawler due to
Pir.
When the Ooze enters the battlefield,
Sigil Captain triggers, putting four +1/+1 counters on it due to
Pir.
Activate
Crystalline Crawler's first ability twice by removing two +1/+1 counters from it, adding ({1} magic symbol) ({G} magic symbol) .
Repeat.
Once you have infinite Oozes with a +1/+1 counter on them, you may remove those counters to create an infinitely large Ooze using