All the monsters...U time.
Like its good friend Q, U has but two monsters:
In the comics, the Hulk got his name 'cause he was marauding around and some soldier said (approximately) "It's some kind of....hulk!" Do you imagine this thing got its name because it waddled out of the shadows and some terrified henchman went "oh no, it's some kind of...hulk! A-and it's umber!"
In recent years, illustrations of the umber hulk have turned it from its original Kirby-esque form into a sort of bipedal giant flea. The original at least has wackiness on it's side, the new one is the kind of thing that'd look really great in the 3d animated giant bug movie but has very little cache in the imagination. The original umber hulk--if we ignore the comic bookiness of the picture-is really not too far from a Bosch demon: it looks at you and you are confused and then it bites you with mandibles. I think my real issue with the hulk as originally presented is that it's treated like an ordinary species rather than some abyssal abomination.
We are all the way down to u, very near the end, so you probably already know--if you've been reading these since the beginning--two things I'll say up front:
-the unicorns I'll use will be nasty or gruesome or gritty or appalling victimized and,
-the girls would desperately like to get their hands on one.
But what else? Long before Christians or even Europeans got ahold of unicorns, their defining feature was untamability--it signified this to every culture that ever dreamed of a horse with a horn. Why?
Well, what's a horse? To the kinds of people who sit around thinking up things to engrave and to symbolize, a horse is an aid to war. You ride on it so you can fight people and the horn is a weapon. In other words, in a unicorn you've got the horse and you've got the sword, so who really needs a guy since all they really do is sit on the horse and hold the sword? It's the premodern equivalent of a tank. So a unicorn very neatly symbolizes self sufficency--it is, if nothing else, independent.
This is perhaps why riding a pegasus into battle seems a little bit less overkill than riding a unicorn. It's actually a kind of interesting paradox: no matter how it's set up, the point of the unicorn is generally going to be that the PCs want the unicorn--but the other point of the unicorn is that the unicorn makes the most sense when it's independent. Doing pretty much the only thing a PC could do with it takes away the very thing that makes it itself.
Most monsters you can only kill their bodies, but a clever enough PC can actually do worse to the unicorn: it can rob it of meaning.