The term MMR:DE refers to a specific Lode Runner project, currently in active development. It's an unofficial built-from-scratch Mad Monks' Revenge (or Lode Runner On-Line) project by QuarkRobot, found here: https://mmr.quarkrobot.com/. The link is also in the Resources tab.

MMR:DE is probably the easiest way to play the game without downloading emulators or abandonware. MMR itself contains the single player levels of TLR, plus additional levels exclusive to MMR, but does not contain the TLR exclusive Co-op levels.

MMR:DE is only allowed for Single Player runs of Lode Runner: The Legend Returns for the above reason. Be sure to mark "DE" for the "MMR:DE?" option when submitting a run.

Oh man that is amazing. I will note that the default settings on the mmr:de version is faster than OG PC version or PS1. I honestly have no idea how to moderate that but it is a nice pace on the remake, if i get around to a full run i'll definitely use that.

That's also a fair point. I love it since it makes the game so accessible, but for no-speed, maybe a specific speed in MMR:DE should be enforced to best match the original game's speed.