0 has no gender, only slime, going by slime/it/they/he pronouns
Similarly, pink uses it/its and has no gender because it's a worm and worms don't need that dumb gender stuff
Devi is nonbinary (+ a lesbian), using they/she
Firenze is transmasc, still deciding pronouns but probably he, maybe they or neos too
Emery is a trans boy and goes by he/him
I'm changing Storm's character to be male, so I'll probably make them trans
There's likely more, but these were the ones that stood out while I was going through them!