Hanenbow is a stage that came back from Brawl on Wii. I can see why they didn’t choose to include it in Smash 4.
It’s based on a “stage” in Electroplankton, a game on Nintendo DS. I actually had it, and it was one of the strangest but interesting games for the DS.
Like the game, you have little electroplankton dancing around and bouncing off leafs.
But I can see why some people would hate it. It’s not a very well designed stage. Even more casual tournaments would probably not let fighters choose this one.