So a while ago I was thinking about posting on this. Just reading through the introductory descriptions of the different forms of fantasy, and then when I came across Liminal Fantasy, I immediately thought of Scott Pilgrim.
I know it's not really urban fantasy like the other things we've read, but it does techincally take place in an urban environment, and there are elements of the fantastic (well, or something... not normal). And now I'm convinced that it is an urban fantasy, but just a liminal fantasy, unlike the intrusion and immerseive fantasies we've read thus far. Liminal meaning that the fantastic isn't really explored. It's present, but it's not a central part of the story, nor is it questioned by the characters. It's really difficult to explain, actually.
"When the fantastic appears, it should be intrusive, disruptive of expectation, but instead while the events themselves might be noteworthy and they may cause chaos, their magical origins barely raise an eyebrow. We are disoriented. The enclosed nature of the immersive fantasy is absent: the hints and cues are missing, but as in immersive fantasy, the protagonist demonstrates no surprise." - Mendelsohn
This very accurately describes Scott Pilgrim, I think. I mean, the evil exes are never questioned (or at least, the fact that Scott has to fight them isn't really), nor is the fact that they explode into change when they die, or the subspace highway through Scott's dreams. These things just happen, are unexplained, throw you off, and then we move on. As Mendelsohn says, it's probably the weirdest, most difficult kind of fantasy to pull off.
As far as it being urban fantasy or not, the book takes a really different kind of fantasy, which I could generically describe as arcade-game style fantasy. Which we probably don't think of as a fantasy, but what else could it be? Science fiction? I think not.
This kind of fantasy actually really reminds me of Bad Monkeys, by Matt Ruff, which is like a... I don't even know. A fantasy that takes mundane things and makes them fantastic: toy guns that can stun or kill people, hallucinogenic drugs that give you superpowers, payphones that you use to communicate with secret organizations. That particular book isn't liminal fantasy, but it is this weird ultra-modern fantasy. Some people would just call it sci fi, but they lack the kind of scientific explanation that scifi has. Or really any kind of scientific inventions or anything.
For those of you who are unfamiliar with Scott Pilgrim, it's really difficult to describe. I would suggest just going out and reading it, because a) you'll actually understand, and b) it's SUCH a great work, and really novel and groundbreaking in so many ways. Seriously, I could write a book about it. READ IT.