"On fire" is more commonly a red ability; maybe just give it a flat "swap P/T"? Blue gets that sometimes.

Blue gears this ability frequently enough.

Often it comes paired with the ability to switch power for toughness as well. But, yeah, I agree with Link. I don't have a problem with blue flowstone on rare occasions.

­Watercourser

I don't think one-off example is that good. That way you could justify Hornet Sting and such.

Gatherer search for modern mono-blue cards with the text " gets +1/-1 until end of turn."

This is quite similar to Metropolis Sprite.

Fair enough. "Get more often" doesn't mean "Can never go there" if you've got a decent reason to want it.

If you happen to need a slightly more fiddly common blue flier in the set; go for it.

Well the main reason is that the ability well captures the fluid nature of a mutant's body.