I found this on the Pokemon site for the aforementioned game's summary:
"Super Smash Bros. Melee debuted to huge fanfare in 2001, and went on to become one of the highest-rated and best-selling titles for the GameCube system.
This sequel to the Nintendo 64 smash hit is also Pikachu's first appearance on the Nintendo GameCube. Super Smash Bros. Melee adds several Pokémon to its growing roster, including the Legendary Pokémon Lucario and Mewtwo, as well as the adorable Baby Pokémon Pichu. Jigglypuff returns to the fray, too.
Stage your battles in several places in Kanto, including the Pokémon Stadium. As the fight goes on, platforms will pop out of the stage, requiring you to adjust constantly for changing conditions. And watch out for Poké Balls that show up as items—they might contain mischievous Pokémon such as the giant Snorlax, whose huge belly bowls over everybody in its way!"
Second paragraph, it says you can use Lucario and Mewtwo. Now unless I've gone crazy, Lucario wasn't released until Gen 4, whereas Melee came out in 2001, before gen 3 was even out. And it couldn't have been a mixup between Melee and Brawl, because Mewtwo isn't a playable character in the latter just as Lucario was not in the former. Is Nintendo prone to errors like this? I've never seen this kind of error from such a large company.