The "freeze whole body thing" is kinda harsh but I think you could say something like "the effect is negated upon any contact with fire" or something more to make it a bit less final (I always had this thing against techniques that put you in a really rough spot and that is completely user controlled without exception).
I would put ultimate at more around 100 training posts though because ultimate truly means MASTERED and well that is a long way away from the level of an average level 4 kidoh in my perspective, but I guess I won't argue on that part too much if you wanna keep it 50.