Lucy, Celestial Wizard

Reach, Vigilance
Whenever another creature you control leaves the battlefield you may pay {x}, where X is that creature's converted mana cost. If you do, put a Celestial Spirit creature that you own from outside of the game onto the battlefield.
You may only control up to 2 Celestial Spirit creatures at once.
If Lucy leaves the battlefield, exile all Celestial Spirit creatures you control.