Dwarf Fortress is a ludicrously insanely complex "game" where you command, wait for it, a fortress of manic-depressive, alcoholic, sociopathic, retarded dwarves. In ASCII graphics.
The "fey mood" was an in-game event where a random dwarf would suddenly feel the burning urge to produce a very specific item, meaning you either had to find a way to acquire a dozen random materials and set up a high-tech workshop to lock Urist McDwarf in, or you had to watch as he flipped out and killed everything inside the fortress, directly or indirectly.
Well, I couldn't be too careful, because my dialect sounds something like this:
Yeah y'all needa be goan down by that trailer with tree growin init, an dhin y'all wanna go down that way for two or three songs until you get by the bridge o'er Injun Creek, an then y'all gonna turn left when y'all get to Big Jim Slucher's cornfield, and then y'all get back on the highway.