[@RainbowFactory] Well everyone ingame refers to them as a he, so I'm just going off what I know. Like Papyrus and Undyne in some of their phone calls. It's highly suggested that he may be trans, but I think it's kind of up for discussion. But even the random Mettaton fans you meet in Hotland call him a he, so I think he's outwardly a guy, just a very feminine one. But you can do what you like, I guess, you're rping him, so you get to make the final call.