I guess I'm predictable.This won't satisfy your desire for self-destruction, though, unless you intentionally take oodles of backlash.
I suppose you could pair this with another custom power to get that effect. You'll probably have to make it yourself, though. And then you might as well make an entirely new power.
But for whatever it's worth, here's an untested and probably unbalanced power from the master list that sort of approximates damaging yourself with magical enhancement.
PAINFUL TRANSFORMATION [+1]
Description: Shifting forms is extremely painful.
Musts: A Shapeshifting ability.
Skills Affected: Endurance
Effects:
Painful Transformation. Choose one form you have access to. Whenever you shift forms, unless it is into the chosen form, you immediately receive a Mild Physical Consequence related to the stress of transformation.