Is 結晶 a verb and a noun? I've seen it being used as a noun for 'crystals' in a game and it's also been used as a verb in the form of 'Kesshou!(crystallize!)' for a superhero transformation call in Spielban. Is simply saying Kesshou normal for using it as a verb or do you normally attach -suru to make Kesshou a verb?

Are you thinking if one might say , or something like that? Then definitely no, itself is a simple noun that never conjugates. (A crystal maniac might try coining such a verb using this pattern as a joke, but I have never heard such a verb.) is still ungrammatical. If you want to say "to crystallize", it's **** (works transitively and intransitively), where () is a suffix like _-ization_.

"!" is too long as a "transformation call", so is a reasonable choice for that. Just because it's used similarly to "!" does not mean it's a verb. Shouting a pure noun is not strange even in English (e.g., "Attention!", "Silence!")