Catboy and Catgirl come from a retro Gameboy title called CATRAP. Sakurai wants to include retro characters, and their game is in the 3DS E-shop. They seem like an interesting pick. Like the Ice Climbers, you control Catboy and Catgirl at the same time.
A ^ Upward Scratch
A V Double Kick
B. Bumper: Like their primary attack from CATRAP, they bump into the enemy.
<-B-> Block Bump: They bump a block to hit the foe.
B ^ Tag Jump: Kinda like the Ice Climber B ^ in Brawl.
B V Time Slow: Catboy and Catgirl slow time around them to make foes easier to hit, however temporary the effects are.
Final Smash: Enemy Rusher
Everyone else on the stage turn into ghost enemies as Ctaboy and Catgirl gain tremendous speed and bump them off with one hit.