DasVergeben says he’s heard from sources the Ice Climbers, Ridley from the Metroid franchise, and Simon Belmont from the Castlevania series are playable characters in Super Smash Bros. Switch. He claims Ridley will be officially announced at E3 2018.
The leaker also shed some light on other aspects of Super Smash Bros. Switch. All fighters from Super Smash Bros. for Nintendo 3DS and Wii U are making a return, so no one’s getting cut. The game is a sequel and art assets will be reused to some extent.
Keep in mind this remains a rumor until Nintendo makes an announcement, so take it with a grain of salt.