Okay then. Matthew's Nightmare. It doesn't have a custom title screen, or anything, it's just... Matthew's Nightmare. (Going by the patch filename, it's Cedar_Ragefest, but no one calls it that.)
This hack, by Cedar of serenesforest, was created for a contest by markyjoe1990. The idea was to "make a funny yet gruesomely hard (but fair) Fire Emblem chapter." And despite being only one chapter, it contains several maps, each with their own horrible gimmicks.
To be clear, it's immediately evident that a lot of effort went into this. It's not something someone just slapped together, it's pretty well-balanced so that you can get through it without ever really resorting to getting lucky. But it is by no means "fair." Certainly, if you know what to do, you can get through it without savestates, and because each part has its own units, random gains from levelups don't really matter. But the key phrase, of course, is "If you know what to do."
The first time you play through it, you are in for some nasty surprises. I don't think anyone can reasonably be expected to play through it blind AND without savestates. My first playthrough took several hours, and there was one point I'm not sure I'd have ever figured out if there wasn't pertinent info in the... Screenshots on the hack's thread on serenes. But to the game's credit, the random "screw you"s are all unique and different. Part of the charm is being surprised by what the game will throw your way next, in an "I Wanna Be The Guy" sort of way. The plotline of the hack, too, is in no way serious, but it also doesn't tread into LOL SO RANDOM XD territory. Usually. There are a few exceptions and they are as grating as you would imagine.
In general, I actually quite like the hack... I just think it's kinda dumb. But enough talking about it - Let's get right into it.