[quote name='tankexmortis']Okay, I give up - what's Megaton? A codename for Mother 3 or something?[/QUOTE]
Again, it's a joke from way back in the Gamecube days.
Basically, there was a rumor that a "megaton-level announcement" was coming. It caused insane amounts of speculation from the Nintendo camp, including the buy-out of Capcom and/or Sega, various game collaborations (A Nintendo-Sega massive RPG title), and other various omfg-we're-all-going-to-die-from-the-blood-loss-from-our-erections predictions.
In the end, it turned out to be something that either A) never happened, or B) was lame, with the official answer being that it was some Japanese magazine's mascot getting their own game, whose name was Megaton. Or something to that effect. Point being was that it was a huge "disappointment" depending on who you are talking to.
So now it's a common joke that anything Nintendo is secretly harboring is teh megaton, or some variation thereof.