Powers are measured on a ‘scale’ of 3 to 18 (3d6), although Power Rolls can be less than 3 or more than 18. When you create a new power, you’ll have to decide what the ‘average’ person with the power can do, at the beginning of their career. If you don’t have many examples to go on (only one comic book character has the power, for example), decide whether you want that example to be weak, average, or powerful, and design the power’s scale around that decision.
Powers should be limited to things that require a definite change in genetics or anatomy to accomplish. If a power could also be a skill, then it shouldn’t be a power. Can people learn this ability, or do they have to undergo some strange sci-psi-magical accident to gain it?