Agatha's Soul Cauldron, Deeproot Pilgrimage, and North Pole Patrol

Prerequisites

• Agatha's Soul Cauldron on the battlefield
• Deeproot Pilgrimage on the battlefield
• North Pole Patrol in exile

Steps

1. Activate the nontoken Merfolk using North Pole Patrol's ability by tapping it
2. Deeproot Pilgrimage triggers, creating a 1/1 Merfolk creature token
3. Resolve the Merfolk's ability, untapping the other creature
4. Activate the other creature using North Pole Patrol's ability by tapping it, untapping the nontoken Merfolk
5. Repeat

Results

• Infinite ETB
• Infinite creature tokens