Awesome update today. I really wanted this feature to be in, I hope other single-player modes can be played cooperatively as well. And another tease by Sakurai at the end, another way to power your characters up, so something like a Smash Ball? The enemies also seem to have their own health-bar?
It seems difficulty levels are different as well. There's no very easy anymore and they added an even harder mode, Intense.
I would hate that, as I have no plans at all to buy that game. If Sonic makes it in he should be unlockable but without using stuff like this. The Olimar trophy annoyed me as well, as I am a bit of a completionist. I got Pikmin eventually but it shouldn't have been necessary.