[@LostButterfly92]Sources of power include but are not limited to being born that way, lab accidents, aliens, and magic.
Pretty common
Powers are determined by whatever you want them to be.
People with powers are susceptible to mutations just like anyone else.
It would depend on how they gained their powers. If it was traumatic, I’m sure that would have an effect. If they were born with it, I’m sure it would have less of an impact.
Aliens are rare, but they do walk among us. The government has more contact than the average person. And yes, you can play an alien.

Think of this world a nice mash between Marvel, DC and popular indie superhero comics. How much of one thing over the other is determined by the players.