Dr. Mario Stage Boss
A source states, "Super Smash Bros. for 3DS/Wii U introduced Stage Bosses to the series. These were new opponents that appeared in certain levels, that would attack all players on the field. The Stage Bosses are the Yellow Devil (from Mega Man), the Dark Emperor (from Find Mii), Metal Face (from Xenoblade Chronicles) and Ridley (from Metroid).
The Stage Bosses are all huge monsters that dwarf the playable characters. They possess unique attacks and cannot be thrown off the stage. In order to defeat a Stage Boss, you need to take their health down to zero (like a traditional fighting game boss). Usually, this grants the player some sort of bonus (like an extra point, if you aren't using stocks). There was another Stage Boss that was planned for the Smash Bros. for 3DS/Wii U. Fans have gone through the data of the game and discovered evidence for a scrapped Dr. Mario stage. There exists character art for the from Dr. Mario. This art is placed among the other Stage Bosses, suggesting that the players would have battled the Viruses at one point"(Baird).
