17 if you count the Koopalings...

Notes:

This is in no way intended to be me slamming the Mario series. It just baffles me that people complain about how there are "Too Many Pokemon" when there are so many Mario characters. Heck, there have always been more Mario characters playable in every Super Smash Bros installment. (Except in Brawl, when they tied…and even then, they have less characters in 4.)

(Even if we If we don't count Donkey Kong…)

SSB64:
Mario: 3 (Mario, Luigi, Yoshi)
Pokemon: 2 (Pikachu, Jigglypuff)

Melee:
Mario: 6 (Mario, Luigi, Peach, Bowser, Yoshi, Dr. Mario)
Pokemon: 4 (Pikachu, Jigglypuff, Pichu, Mewtwo)

Brawl:
Mario: 6 (Mario, Luigi, Peach, Bowser, Yoshi, Wario)
Pokemon: 6 (if we count the Pokemon Trainer's Pokemon; Pikachu, Jigglypuff, Lucario, Squirtle, Ivysaur, Charizard)

4:
Mario: 9 (Mario, Luigi, Peach, Bowser, Yoshi, Wario, Rosalina/Luma, Bowser Jr, Dr Mario)
Pokemon: 5 (Pikachu, Jigglypuff, Charizard, Greninja, Mewtwo)

Sorry if I got a little ranty. I've been wanting to say this for a while. More SSB Fandom insanity.