Mercy

Seeing no reason to mess with success, especially now that the giants have given up on throwing rocks at her, Mercy shifts her horse back and to the edge of the wall, and lets fly with another fireball. Seeing what she hopes is one of Smokey's allies descend from above to join the fight, Mercy aims so as to miss the floater.

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Moving the horse diagonally back from the wall of goo, and to just past its edge - about 20' back, to give LMM and War Machine plenty of room in front of her as desired.

Fireball: (10d6+3)[32]. Still reflex 19 to save. First priority is missing the elemental, then hitting as many of them as possible.