I feel like I've just walked into a random stranger's birthday party, lol.
Anyway, I have some stage ideas:
N's Castle:The area with the blue carpet where you face Reshiram/Zekrom in Black 1/White 1. Like the Bridge of Eldin you can't fall to your K.O. The roof has collapsed and you can see Dragon Spiral tower outside. Occasionally, you can also see New Team Plasma's ship fly past. Similar to Spear Pillar, at the start of the stage Reshiram/Zekrom/Black Kyurem/White Kyurem will sit on a throne in the background and use their signature moves which effect the stage in different ways.
The New Frontier:A desert with a town in the left of the background. Like before, you can't fall. Sometimes a den will appear and a grock will emerge and walk across the screen, dealing damage to anyone who touches it. If Dillon is not being played as, sometimes a silhouette of him will roll across the background. Also, one of those grocks with a crystal on its chin (I forget its name) will sometimes grow out of the ground and shoot fighters with explosive rocks.