I had an idea of having a star/plasma transformation quirk, where my character could transform into a walking being a pure plasma. It would start at the color red then depending on how [i]heated[/i] the battle would get she can get progressively more powerful which is indicated by color starting with red, then, yellow, white, and finally blue. Then there is her final form which she calls her “nova” form. 

These forms give her an increase in speed and strength at the cost of energy and her own mortality. The [i]hotter[/i] she gets the better the increase of stats but the greater the cost and the longer she stays in the form the more likely she is to just collapse from exhaustion or even the possibility of death if she pushes herself to hard.