The original answer is below me. Nintendo asked Capcom for permission to have Megaman in Brawl. There are rumors that they asked for Zero as well, if not as a character then as an assist trophy. Nintendo had already gotten a lot of progress on making Megaman's character for Brawl, but were suprised when Capcom refused to allow them to use Megaman or Zero in the game. SSBB is solely a Nintendo game. With the exception of Snake and Sonic, there are no other third-party characters (including Capcom characters)
No, Megaman will not be in and is not in Super Smash Brothers Brawl.
It's spelled MegaMan, & no.
No, Pichu is not a playable character in Super Smash Bros Brawl
What character?
Shadow is not a character in Super Smash Bros Brawl, unfortunately.
Midna is not a playable character in Super Smash Bros Brawl
No, Jack Skellington is not a playable character in Super Smash Bros. Brawl.
Mewtwo is not a character in Brawl
Tabuu is not an unlockable character on Brawl.
Oh, but he is now. Mega Man will be in the next Super Smash Bros. games, Super Smash Bros. for Wii U and Super Smash Bros. for Nintendo 3DS. The reason he was not included in Brawl (or previous SSB games) is likely that there was no room for him: an agreement with Capcom, if one was sought, could not be reached until the game was too far into development for his inclusion.
mewtwo is not in super smash bros. brawl however mew is a trophy character
Groudon is in Super Smash Bros. Brawl as a Poke Ballsummon, but not as a playable character.