Transgenderism is a thing, but I don't think it's a gender, as it is simply a person that is one and identities as another. I don't think that someone can actually change their sex, no matter what hormones they take, or cuts they make. I see Gender dysphoria the same as body dysphoria, like anorexia. It's a mental illness that should be met with understanding, and treatment. It really bugs me when the mainstream view in the West is that we should encourage enabling it. Also, people under 18 should never have reassignment surgery or hormone blockers, as they cannot consent to such a life changing procedure, and the consequences of both are irreversible.
Other than that, there can exist girlish boys and boyish girls. That however, does not make them the opposite sex...
All this tumblr shit about 300+ genders is bs. It's a fad and it'll pass soon enough.