Activate Celestial Unicorn by using Walking Ballista's ability by removing a +1/+1 counter from it, dealing 1 damage to any target and causing you to gain 1 life due to its lifelink.
Celestial Unicorn triggers, putting a +1/+1 counter on it.
Repeat.

Infinite damage

Infinite lifegain triggers

Infinite lifegain

Agatha's Soul Cauldron

Walking Ballista

Celestial Unicorn

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

Combos with "Celestial Unicorn"