I know I'd definitely want to bring Raz (Psychonauts). He's just so much fun! Maybe I'd bring along Sasha and Milla for good measure; Sasha can linger in the corner of my own party with me while Milla sets it up and turns it into a REAL party!
Also assuming we can communitate, I'd TOTALLY want to invite Spyro (the Tom Kenny one, not the Elijah Wood) and and Toon Link. What can I say, in a non-creepy way, kids just liven up parties and I'm basically kid enough (ALL NIGHT PLAYING BRAWL, WHAT WHAT) that it'll all be a good time. Maybe Ellie from Last of Us. AND LEE AND CLEMENTINE I FORGOT
On the opposite end, if we're talking adults, I'd probably want to invite like the four dudes from Catherine(Jonny, Vincent, Toby and Orlando) because they're just so lax.
I like the former though because I need Milla to liven up my party and we'd all wear buttons that say how happy we are to be there