Hanenbow

Arguably one of the best stages in the entire Super Smash Bros franchise. It is based on the Experimental Music Game Electroplankton on the Nintendo DS, specifically the part with the, well Hanenbow: little Tadpole-Like creature who produce sounds when hitting differently angled leaves and the water surface. It first appeared in Super Smash Bros Brawl for the Nintendo Wii when it was an unlockable stage after clearing the 28th Event: Flower Blooms in the Echoes in any difficulty. It had a unique particularity: there was no music to choose, and instead had an ambience piece in the background to go along the sounds produce by the planktons themselves. It is available from the start in it's reappearance in Super Smash Bros Ultimate, just like every Non-DLC stages, and it also got a new Remix cointaining the different sounds produce by the Hanenbow, Luminaria, Lumiloop and Beatnes (It's a banger by the way.)