Should only need 3 worldfires, don't want one in opening hand after all.

608.2i If an ability's effect refers to a specific untargeted object that has been previously referred to by that ability's cost or trigger condition, it still affects that object even if the object has changed characteristics.
Example: Wall of Tears says "Whenever Wall of Tears blocks a creature, return that creature to its owner's hand at end of combat." If Wall of Tears blocks a creature, then that creature ceases to be a creature before the triggered ability resolves, the permanent will still be returned to its owner's hand.