Um, I am not going to download if it seems bad. Just provide a couple screenshots or something, it's not that hard to load it up in an emulator.

you cannot add backgrounds to SMB underground unless you use ASM (code editing) or if you want to replace it with another theme's background with byaml editing.

It's for all the backgrounds that are black.

Very complicated, I might be able to shrink the steps down with a bit of Hex Editing, but overall this is pretty cool!

Most friendly Samplasion
Most helpful MasterVermilli0n
Most creative Buntendo
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Best copycat
Most relaxed tee
Happiest The Mario Modder

Best regular user
Best staff member NightYoshi370
Best banned user (do not nominate tempbanned users) theninja1000

Best username zachabossaloler
Best avatar Sm-ArtThings
Best post layout Buntendo
Most likely to break the board with their post layout GRAnimated
Best bio explos

Best artist Buntendo
Best programmer MasterVermilli0n
Laziest GRAnimated
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Most likely to appear at random MasterVermilli0n
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Best potential leader Buntendo
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Best level designer TheNawab
Best Mod Maker Buntendo
Most likely to make a level with a 0.01% clear rate TheNawab
Most likely to die at the last second without a checkpoint Toms
Most likely to spamvertise their custom theme

There are two pixels of padding on the edge of every block in the tileset.

Stuff like this takes a lot of time.