I'm sorry to be that guy, but Button mash is not exactly an OC. He's actually a one-shot backgrond pony that appeared in one of the show's episodes (which one I can't remember: I left the Bronies long ago).
Minus his look however, all the rest is original to Button's adventures!
Luna: I'll show you how a seasoned pro plays! Button: Seasoned? You only played since what? Two years? I played four! Luna: Quiet you little insolent! I have experience beyond any other living pony and you'll see who's the most seasoned here! Button: Yeah, yeah... Blah blah... You are still a newbie here. Let ME show you how to play like a pro! Luna: Why you.... Don't you have any respect for your elders? Button: Did you just confirmed that you are older and slowed than me? Luna: Grrrrr! I'll destroy like the little.... Hey! The image disappeared! Button: Huh? I was sure the console worked perfectly. Give me a moment your highness, I'll check what's wrong. Luna: Take your time, darling. It would be sad to end this game so abruptly, when we were have so much fun. Button: Yeah. Let me see... Oh! It was only the wiring. There you go. Luna: Huzzah! We can play some more! Ummm... Button: What's wrong princess... Luna: Luna. Call me Luna. Button: Okay. What's wrong Luna? Luna: Don't you feel that is.... weird... to play at a videogame with a princess at your side? Button: What? No way! It is so cool! We beated those newbies together like nothing thanks to those tricks you teached me. Luna: Oh! I'm relieved. I never expected youngsters like you to be this at ease with me that way. Button: Nah! Like I said you are cool. And very good at videogames. Now, let's finish this game. You are going down! Luna: Not before I crush you like a bug!