Board Thread:Questions and Answers/@comment-39106664-20190420011352/@comment-35757757-20190909111750

Let’s see her:

“Dear Diary: Shyren's sister ‘fell down’ recently. It's sad. Without her sister to speak for her... she's become more reclusive than ever. So I reached out to her, and told her... that she, Blooky, and I should all perform together sometime. She seemed to like that idea”

Never says anything about Mettaton being a girl. Just because he wanted to hang out with a girl doesn’t mean he was one. I’ve hung out with boys before, but it doesn’t mean I’m a boy.

“Dearer Diary: I like to buy a new diary for every entry I make. I love to collect diaries.“

Nothing about gender here either. There’s nothing stopping a guy from getting a diary, and not all girls will have one (I don’t)

“Dearest Diary: Our cousin left the farm to become a training dummy. That leaves just Blooky and I. Blooky asked me if I was going to try to become corporeal, too. They sounded so... resigned... come on, Blooky. You know I'd never leave you behind. And besides... I'd never find the kind of body I'm looking for, anyway.”

Nothing about gender again. Even refers to Blooky as a they, like all ghosts without bodies are in Undertale, meaning Mettaton couldn’t have had a gender before, and when he does get a body he’s been referred to as male by everyone, including Alphys herself and the flavor text

“My Darling Diary: I met someone... interesting today. Last week I posted that advertisement for my Human Fanclub. Today was our first meeting. Only one other person came. Honestly, she's a dork. And she's obsessed with these awful cartoons. But she's kind of funny, too.... I want to see her again.”

Hey look: NOTHING ABOUT GENDER

It’s a club, and nothing says it was girls only. He could definitely join.

“Diary... My dear: My diary collection is going fabulously. I have like five now.”

Again, since there is nothing stopping a guy from getting a diary (and he was a genderless ghost before), this means nothing

“ Dear Diary: She surprised me with something today. Sketches of a body that she wants to create for me... a form beyond my wildest fantasies. In a form like that, I could finally feel like... ‘myself.’ After all, there's no way I can be a star the way I am now. Sorry, Blooky. My dreams can't wait for anyone...”

Nothing about gender!

HE IS LITERALLY REFERRED TO AS MALE BY EVERYONE AND NEVER HAS A PROBLEM WITH IT! READ THE FLAVOR TEXT!

I’ll even put them in bold!

Normal form flavor text:

“His metal body renders him invulnerable to attack”

“His metal body STILL renders him invulnerable to attack”

“Seriously, his metal body is invulnerable!”

EX:

“His weak point is his heart-shaped core”

“Mettaton EX makes his premiere!”

Look on the wiki page for yourself!

https://undertale.fandom.com/wiki/Mettaton/In_Battle

Or play the game and read the flavor text!