The very first video game I owned was Kirby's Dream Land 2 on Game Boy. I loved that game, lost track of how many times I finished it, and since then I've tried to own or at least play as many Kirby games as I can, they're great fun, if a little kiddy. For an eight-inch tall ball of marshmallow, Kirby is a rampaging engine of destruction, battling elder gods and ancient threats whilst devouring his foe's very souls to gain their power. In game terms, I'm not entirely sure how Kirby would work, his whole "inhale and copy" ability would be odd in a 3D miniatures game, I think it would be a bit of fun, however, to have this pint-sized, pink "Star Warrior" tangling with the likes of Thanos.
2. Commander Keen
4. Samus Aran
I haven't played many Metroid games, but I have a soft spot for Samus; the bastard daughter of Ellen Ripley and Tony Stark. Like all Nintendo characters, Samus has had a grand destiny built upon her in recent years, but back in the day, she was just a damn talented bounty hunter with the bad luck to keep getting caught in the middle of an alien holocaust. Forget the sexed-up "Zero Suit", I want to see an armoured Samus blasting away Skrulls on my table one day, hoping she gets paid for saving the day yet again.
Why has there never been a Megaman/Astro Boy team up? In the distant year 20XX, the evil Doctor Wiley attempts to conquer the world with his invincible Robot Masters; the only thing in his way, Doctor Light's robot boy, Rock. Endlessly adaptable, almost indestructible and (depending on how you read Bob and George), pretty stupid, Megaman has been a gaming icon for decades, and has always had that superhero edge to his story. Not sure how his various powers could be represented, but I think he'd be a popular addition to any games featuring Metallo or Ultron.