Primal Prayers + Guide of Souls + Cavern Harpy

Primal Prayers

Guide of Souls

Cavern Harpy

How it works

1. Cast Cavern Harpy by paying E due to Primal Prayers, if able, or by paying its mana cost.
2. When Cavern Harpy enters the battlefield, it and Guide of Souls trigger.
3. Resolve the Guide of Souls trigger, causing you to get E and gain 1 life.
4. Resolve the Cavern Harpy trigger, returning it from the battlefield to your hand.
5. Repeat.