Agatha's Soul Cauldron, Spike Feeder, and Celestial Unicorn

Prerequisites

• Agatha's Soul Cauldron on the battlefield
• Spike Feeder in exile
• Celestial Unicorn on the battlefield
• Celestial Unicorn has at least one +1/+1 counter on it

Steps

1. Activate Celestial Unicorn using Spike Feeder's second ability by removing a +1/+1 counter from it, causing you to gain 2 life
2. Celestial Unicorn triggers, putting a +1/+1 counter on it
3. Repeat

Results

• Infinite lifegain
• Infinite lifegain triggers