Great game, really, this is the best Smash Bros fangame on the internet right now. I play it with my Gamepad using JoyToKey and I must say it really feels professional.
Here are a few bugs I found, I don't know if they have been already reported.
First, Hyrule Castle needs larger barriers because Kirby can jump as high as he can off the top platform and kill himself..
Second, I was doing an all random free for all at a random stage, after the match was over, I took players 3 and 4 off and only had players 1 and 2 on a character. When the match started, players 3 and 4 showed up as another random character, it did this until I left to the menu and went back to character select, then it stopped.
About Mewtwo:
Why take out Mewtwo because the SSF2 devs had a stroke that you used their sprite, what are they gonna do? sue? Mewtwo isn't their character. Its really a complement that you use their sprite, because its good. But I won't complain, you guys are dealing with it.