Agatha's Soul Cauldron, Deeproot Pilgrimage, and Tidewater Minion

Prerequisites

• Agatha's Soul Cauldron on the battlefield
• Deeproot Pilgrimage on the battlefield
• Tidewater Minion in exile

Steps

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

Results

• Infinite ETB
• Infinite creature tokens