"Dark" fits best.
People fixate on types as if they mean one, and only one absolute thing, when in reality types convey a multitude of things. It wouldn't make sense to limit themselves in that way.. if they wanted to create a fungus, itd make more sense to just group it in with Grass instead of making a "Fungi type".
Dark types encompass dirty fighting (Payback, Sucker Punch, etc..), the brutality of nature (Hydreigon, Tyranitar. etc...), and literal darkness (Umbreon, Night Daze, etc..). There is some overlap with Ghosts, as a lot of Ghosts are actively damning to the living ("evil"), and are also associated with the night.
"Dark" is a good catch-all for that type, as dark can refer to both a tone and actual measure of light. It fits well.
