It'll take some while till I get there, but the coolest powers I have in my project are the manipulation of time and space. One character can create portals and shoots beams by overlapping them or even storing things in a pocket dimension. The other can stop time, predict enemies' movements and even travels back through time at one point for character development.
But those powers also come with great risk, since overusing them too much can result in death. And for the time travelling one, it will cause massive paradoxes.
Another insane thing a character of mine can do is pretty much comparable to Itachi's genjutsu, but he can only do it by using his seperate energy source, which has a will of its own. The perfect recipe for chaos! xP
And of course, power-ups, can't miss that with shonen fights and I got quite a handful of cool ones that I wanna surprise people with! 