Shortstar took it upon himself to take several levels from RMN Bros and add his own touch to them. Some are adding segments in the middle or end of a level, expanding it, or reworking it from the ground up with the goal of improving the level. Not all levels were changed, but I updated the hub world so remixed levels are marked with a REMIX and a ??/5 difficulty but I didn't change their location. You can snag it under the downloads tab or from this link. For more SMBX fun you can check out Shortstar's own SMBX games here on RMN!
Here's the list of levels changed for the curious in alphabetical order:
A Very Regal Mario
Ankle Biter Forest
Giga Underground Way