Been using this stage for a while now; overall, I enjoy it. The area transitions are pretty neat, and I like Flowey's little appearance at the start of each round. There are a few problems I've noticed, however. For instance, the area transition effect doesn't cover the entire stage:

Spoiler, click to toggle visibilty

Additionally, there's a whole lot of vertical space in the stage, yet most of it is pure black; in fact, the background cuts off noticeably on Snowdin and Hotland. (This cutoff is also noticeable on Waterfall, though not as glaringly.) Only the Ruins have much to see above ground level, and even then there's still a lot of empty space; on all areas, you can't see any of the background at the highest point in the stage (not demonstrated in the screenshots below):

Spoiler, click to toggle visibilty

(Also note the stray pink pixel next to Grillby's.)

Finally, the Survival results screen (and I believe, by extension, the Arcade Continue/Congratulations screens) isn't properly aligned, centering well above the player:

Spoiler, click to toggle visibilty

Overall, I like the stage enough to keep it in my Mugen, and I appreciate the effort put into it, but it could use some refinement.

(I'm using Mugen 1.1 with a game resolution of 1920x1080, in case that significantly affects anything.)

boundleft and boundright are respectively the left and right bounds of the stage. You should always have their absolute value being the same value. In short, you should ALWAYS have boundright = -boundleft. If you don't, your stage will not be symmetric, which means that a player will have an advantage over the other at the beginning of the fight, since one of them can be cornered more easily. This effect is less important on very wide stages, but a stage should always be symmetric, for the sake of clean coding and showing you know what you're doing.