bat bomb

as you pull your hand back, a metal orb begins to materialize above your palm. When it reaches the apex of its arc of travel, the metal orb bursts. Upon bursting 1d100 bats will be summoned. These bats continue the original arc of travel. Upon impact with any object that is not a bat, these bats explode dealing 2d8 damage with no save chance. This explosion covers 10 ft and if multiple bats hit the same object, the damage is equal to 2d8 x # of bats. Upon conjuration, roll a d20, if a 1 or 2, the object explodes in your face dealing 2d8 x 1d100 fire damage. 

Base damage type is force or fire, as chosen by caster