So,after the release on japan,a lot of information started to circulate about the new 3DS stages over smash communities,some of them has something called stage bosses,not many of them are ingame,actually only 4 stages has this new gimmick these ones are:
Willy´s Castle-Yellow Devil
Find Mii-Dark Emperor
Magicant-Flying Man
Pac Maze- The four pacman ghosts
Each one has a different way to defeat or assist the player:
Yellow Devil has a weak spot on the eye,and the player which gets last deals extra damage on his oponents
Dark emperor can change status for certain players with different colors but can leave the arena if the mii on the cage is released.
The flying man can assist the player which summons him first.
The pacman ghosts wander around the scenario but can be defeated by the player who gets the power pellet after collecting 100 pac dots.
Before smash 4 we had things like this but in a very simple way in the cases of Mario Bros Stage on Brawl,who had some enemies like the turtles/crabs easily defeatable.
Willy´s Castle-Yellow Devil

Find Mii-Dark Emperor

Magicant-Flying Man

Pac Maze- The four pacman ghosts

Each one has a different way to defeat or assist the player:
Yellow Devil has a weak spot on the eye,and the player which gets last deals extra damage on his oponents
Dark emperor can change status for certain players with different colors but can leave the arena if the mii on the cage is released.
The flying man can assist the player which summons him first.
The pacman ghosts wander around the scenario but can be defeated by the player who gets the power pellet after collecting 100 pac dots.
Before smash 4 we had things like this but in a very simple way in the cases of Mario Bros Stage on Brawl,who had some enemies like the turtles/crabs easily defeatable.