Enormous Fly Swatter

Target a 15'x15' area within range that you can see, you conjure an enormous fly swatter 15'x15' that floats 10' above the target area.    The swatter then smashes that area, all creatures in the area must make a dexterity save or take 3d10 damage, half damage on save.  Additionally, any creature that fails its save must make a strength save or be grappled by the swatter, creatures may repeat there save at the end of their turn to escape.  Grappled creatures take full damage when the swatter swats again.  On your turn you may move the swatter 20' and repeat the attack.  Spell ends if the swatter is ever out of the spell range.  For every spell level above 3rd that is used to cast this spell, the swatter does 1d10 more damage.