In Nethack, playing on a Friday the 13th gives you a luck penalty. Playing when it's a new moon leads to a few interesting mechanical changes.

Friday after next is both October 13 *and* a new moon!

Are you gonna show off your Nethack skills on this spooooky rare day?

Credit for bringing our attention to this delightful occurrence goes to https://cohost.org/0xabad1dea/post/3062685-it-s-coming
@roguelike_con @alexr nethack is one of those games I think more people should write about. I find its absence from various lists of all time important games sometimes befuddling.
@Rycaut @roguelike_con So much energy around Diablo when I view D1 as a graphics-improved clone of ularn.
@Rycaut @roguelike_con @alexr and Hack, and Larn. Everyone talks about “roguelikes”, but nobody talks about Rogue.
@roguelike_con I am playing since last millennium and never ascended with the Amulet of Yendor (not even came close), so I need any bit of luck I can get!
@roguelike_con
I've never looked into the source for this one, but I remember seeing this message in-game and I assumed that it meant something like this :marseyspooky:
@roguelike_con If by show off my nethack skills you mean die on like floor 7 then yeah, maybe