Morphic Resistance

Achilles Heel: Morphic Resistance by Senator Cybus

Note: this Heel is intended for Mega Heroes with powers that rely on physical transformation; Lycanthropy, Growth, any of the Alter Physical Structure powers, etc.
Unlike most shape-changers, the Mega Hero with this flaw finds transformation difficult and profoundly painful. It takes him one full minute to shift into another form, during which time he experiences the agony of his bones, muscles and flesh being forced into an unnatural state. The hero must successfully save vs. pain (12 or higher; M.E. bonuses are applicable), or spend the next 1D4 melee rounds curled up in an agonized, whimpering heap.
In an emergency, the super being can accelerate the transformation and complete the change in just one melee round, but the experience is even more excruciating: the hero must roll 16 or higher to save vs. pain (M.E. bonuses still apply) or suffer the same penalty as above. Additionally, whether the save is successful or not, the super being loses 2D6+2 Hit Points.