Meloetta has been confirmed to be included in the upcoming Super Smash Bros for the Nintendo Wii U. Masahiro Sakurai (桜井政博), Director of the game, announced on Miiverse that all the revealed Pokémon in the Super Smash Bros. Direct Video from April 8th, 2014 will also make an appearance in the game.

This means the following Pokémon are now included in Super Smash Bros: Inkay, Swirlix, Snivy, Oshawott, Suicune. Latias and Lugia were revealed in screenshots in April but are now confirmed for sure as they are also in the trailer.

Miiverse Post

Remember the video that introduced Greninja joining the battle? Every Pokémon that appeared in that video will make some kind of appearance in Super Smash Bros! By the way, here's one of the Pokémon that didn't make an appearance in that video--Meloetta. Its vocal attacks reflect off land forms, so they'll be especially effective in a closed environment.

Source: https://miiverse.nintendo.net/posts/AYMHAAACAAAYUKlXkubnAQ