Agatha's Soul Cauldron, Deeproot Pilgrimage, and Ioreth of the Healing House

Prerequisites

• Agatha's Soul Cauldron on the battlefield
• Deeproot Pilgrimage on the battlefield
• Ioreth of the Healing House in exile

Steps

1. Activate the nontoken Merfolk using Ioreth of the Healing House'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 Ioreth of the Healing House's ability by tapping it, untapping the nontoken Merfolk
5. Repeat

Results

• Infinite ETB
• Infinite creature tokens
• Infinite untap of legendary creatures you control
• Infinite mana legendary creatures you control can produce