Thopter Squadron, Crystalline Crawler, Panharmonicon, and Mm'menon, Uthros Exile

Prerequisites

• Thopter Squadron on the battlefield
• Crystalline Crawler on the battlefield
• Panharmonicon on the battlefield
• Mm'menon, Uthros Exile on the battlefield
• available

Steps

1. Activate Thopter Squadron's first ability by paying and removing a +1/+1 counter from it, creating a 1/1 Thopter artifact creature token
2. When the Thopter enters, Mm'menon triggers twice due to Panharmonicon, putting a +1/+1 counter on Thopter Squadron and Crystalline Crawler
3. Activate Crystalline Crawler by removing a +1/+1 counter from it, adding
4. Repeat

Results

• Infinite ETB
• Infinite creature tokens