No
As a playable character, no.
Ridley is unable to be unlocked as a playable character. The Trophy pops up in the Ridley boss fight, though.
No, Jack Skellington is not a playable character in Super Smash Bros. Brawl.
Ridley is not an unlockable character in Super Smash Brothers Brawl. However there is an internet modification community that has created Ridley as a playable character however adding Ridley requires "Homebrewing" (a.k.a. hacking) the Nintendo Wii and installing unofficial firmware. The quality and playability of the modification is not to the standards of official characters.
No. Tom Nook is not a playable character in Brawl.
No. Naruto is not a playable character.
No, Pichu is not a playable character in Super Smash Bros Brawl
Ridley isn't playable in brawl but can be battled in boss battles or the subspace emissary.
Midna is not a playable character in Super Smash Bros Brawl
WALL-E is not a playable character in Super Smash Bros. Brawl. You are most likely referring to R.O.B.
She is, but not as a playable character.
No he is not a playable character.