Easy. The power to make everything i wish into reality. Be it new power or whatever, i grant it. basically omnipotent
I suppose I'll be your nemesis as I'll channel the unimaginable.
But wait, if you observe me channeling the unimaginable, does it then become imaginable to you? If it doesn't, then I wouldn't even know what's happening when I channeled it, but the fact that it's a superpower makes it possible so I would just cuz I say so and it's what I choose as my superpower.
But, then, my whole superpower falls under the category of your superpower because although the concept of the unimaginable being what it is makes it not able to be imagined, you can still want it, which you could turn into reality because yours is the power of turning what you want, not what you can imagine, into reality. But, can we actually want something if we can't imagine it?
If the unimaginable is a non-exhaustive description of a concept rather than an actual concept, and part of the description is unimaginable other than a vague abstract description defined by the limits of our imagination, then wanting what we can't imagine is possible, and thus you could turn it into reality.
But, if the unimaginable is already reality, which it would have to be to be manipulated, then if you were to wish it into reality, nothing would change for you. If you tried to circumvent that issue by saying you wanted to channel the unimaginable, you wouldn't be capable since your power is simply turning things into reality.
Furthermore, this negates the implied wish of your superpower. Were you to wish for new power to become reality, like you said, then simply imagining new power would be how it becomes reality, you say, "I want to turn the ability to fly into reality." and you imagine yourself flying, and your wish is granted. So, you have the power of thought, basically, or just your same-old imagination, excepting the additional ability to;
Channel the unimaginable, doing so would simply make the unimaginable become imaginable. So I would become instantly omnipotent, and you would too if you wished the same thing. I'll add an addendum to my superpower; "at will" cuz it seems like the sort of thing that might get overwhelming.
So in conclusion our superpowers are the same thing: omnipotence at will.
ok there's some faulty logic in this post, not even including the logical fault in logic itself, so,
My superpower is to have a mug of beer that never becomes empty.