Distant Planet has been in the series since Brawl on Wii. It's based on the Pikmin games, where Captain Olimar travels to a distant planet.
The stage gets pretty basic until the hazards show up. The heavy rain is the most notable. Once the rain hits, being on the slide/cliff is not a good idea.
You also have a Pikmin monster show up on the far-right side of the screen. You can fight on him as a platform, but he can eat you. Then you perish.
While not my favorite stage, I'm glad to see it back in Ultimate. It wasn't in the WiiU version of Smash 4 so I'm thankful it didn't get left out this time.