I was originally going to say Hyrule Castle from the first Super Smash Bros. but we already have it as a DLC stage, so I'm fine with that. However, there is another stage that I want back, and that is the Mushroom Kingdom stage which is also from the first Super Smash Bros. game. I enjoyed playing that game because it sort of a Mario level with some power ups and hazards in it. Even hitting the POW block was fun.