I have the power to stop any attack by throwing myself in front of it.
I am: The Human Shield!
unfortunately, I don't have invulnerability or a healing factor.
or:
I have the power to kill everyone in one try, but that really means EVERYBODY! no exceptions, and I can only kill absolutely everybody, so I'd go like "Yeah, I could easily stop that purse-snatcher, but....I really shouldn't you know."
:/