Mirrored level wad?

My buddy said he heard something about a wad that had the original levels (which "original" game I don't know) mirrored. My limited ideas for google searches have turned up nothing. Any ideas?

Don't know about mirrored wads off-hand, apart from one that's upside-down. There was an April Fools Day hack of Chocolate Doom in 2008 that rendered maps as mirror images but I can't find a download for it right now, unless you're prepared to raid the SVN repository and build revision 1109.

And six years before that there was MOOD.

Sweet, hopefully it works without any issue. I think I'll play at least through e1 this weekend.

some levels of memorial.wad have that property

Played through e1 with my buddy yesterday. It was a pretty cool novelty for e1m1, but after that it just got frustrating. When we'd make a wrong turn and realize it right away it was funny though. I'll never do it again but I would recommend it once.