Baleful Polymorph

The saving throw changes to Fortitude (partial) and Will (partial). A creature that fails the Fortitude save automatically fails the Will save. A target with the shapechanger subtype that fails its save can't use its shapechanging to shift out of its new form. A creature that succeeds at the Fortitude save is partially transformed into the intended animal. For 1 minute per level, it takes on cosmetic features appropriate to that animal and becomes one size category closer to the animal's size.

Augmented (9th): If you expend four uses of mythic power, the spell affects all other creatures with 8 Hit Dice or fewer in a 1-mile radius. Affected creatures transform into Small or smaller animals appropriate to the local environment. You can select a number of creatures up to your tier to not be affected.