Miirym, Sentinel Wyrm, and Changeling Berserker

Prerequisites

• Miirym, Sentinel Wyrm on the battlefield
• Changeling Berserker in hand
• available

Steps

1. Cast Changeling Berserker by paying its mana cost
2. When Changeling Berserker enters, its champion ability and Miirym trigger
3. Resolve the Miirym trigger, creating a token copy of Changeling Berserker
4. When the Changeling Berserker token enters, its champion ability triggers, exiling the nontoken Changeling Berserker until the token Changeling Berserker leaves the battlefield
5. Resolve the Changeling Berserker trigger from step 2, exiling the token Changeling Berserker
6. The token Changeling Berserker leaves the battlefield, returning the nontoken Changeling Berserker from exile to the battlefield
7. Repeat from step 2

Results

• Infinite creature ETB
• Infinite creature LTB