[@Holy Soldier]So his stone-skin and his "take on the properties of other stone-types" is actually a combined quirk? If that's the case, it's probably fine, but because you mention the Emerald Knight and other things coming into play later, I feel like I should probably know what these things are ahead of time. If you're concerned about "spoilers," just send me a PM.

[@Lmpkio]If he's stuck in his transformed state all the time, then the plasma breath and camouflage can probably be handwaved as "biological" abilities of the form that he's turned into. With his four limits, and given that villains are expected to be a little more powerful than the students, he's good to go.