No, I'm not talking about the rugged character making puns about zombies as he blasts the head of a ghoul with a shotgun made from scrap metal and vampire teeth. I'm talking about suspensful comedy. Wipe that "Wtf?" look of your face; it could work. Imagine this. You're reading a really, really scary novel. Say... a Stephen King novel. Then suddenly a paladin springs out of nowhere and banishes the evil monster to nowhere. The characters are all relieved and laughing, and as a vent they talk and joke and chuckle and sing. They have a pillow fight, something to indulge in that they couldn't ever since The Darkness arrived. Then suddenly somebody realizes the paladin went missing. Seriously, just imagine it. Your "THANK GOD THAT CRAP WAS OVER", and then the paladin went missing. Wouldn't it be a good way to scare the pants off your reader? Personally, I'd throw the book out the window, switch on all the lights and curl up in the fetal position until my mother comes back home.
I'm afraid if a horror book took that kind of turn I'd most likely stop short, go back reread the entire chapter to make sure I didn't miss something, then probably have the "wtf?" look on my face. But it'd definately be something different.
For reference, see An American Werewolf in Paris. It's hard to believe that acting in the late 90's could actually be worse than that of the early 80's, but An American Werewolf in Paris manages just that feat, failing to live up to any of the expectations provided by its predecessor, An American Werewolf in London. While the earlier (1981), John Landis directed, film took a very serious approach, it left viewers who came back in 1997 with the expectation of a vicious horror film which let them down horribly. The later film itself is too much of a comedy to be a good horror, and far too much of a bad romance to be a good comedy, and coupled with the terrible acting and shocking French accents, it is a case of absolutely abhorrent film. No, that's not quoted from anywhere, and yes, it's true. An American Werewolf in Paris cuts off from horror at random tangents just to provide humour or romance, things which were very popular in the late 90's (I should know, I was five whole years old when it came out). Of course, it's a terrible mix, and it's only saved by a mildly amazing climax, and then it's ruined again with the ending scene. It lets the American Werewolf story down horribly by adding in new ideas which weren't added in the first one, and, again, with the romance and comedy aspects. Tl;dr? Comedy and horror do not mix.
Turning horror into comedy suddenly, part-way through sounds like a recipe for annoying readers. Making it clear from the outset that you're mixing them and it could work -- a sort of "ha ha -- oh!" effect.
You should watch the monster movies from the 80s and 90s like Critters and Gremlins. Critters is one of my favorites, and even today it's quite scary at times. Well, sort of. The whole concept is that small furballs from outer space (I know...) escape from an intergalactic prison, escape to Earth in a stolen space ship and are chased by shapeshifting bounty hunters. (this really isn't looking good, I know... but it's a great movie! Honest!) The point is these furballs, or Critters, are small, hairy and kinda cute, and they don't mind a bit of slapstick comedy and funny jokes now and then. And who can forget the "I'm a bounty huuunter!" quote? Awesome stuff, and quite funny. But despite even the monsters being cute and funny, they can also be quite scary at times. The same goes for Gremlins. It wasn't as scary as Critters, but it sure had it's moment. Even so, who didn't want a Gizmo-doll after they watched it? (trivia: Critters 3 had a certain kid named Leonardo DeCaprio in his first movie.)
So how about this:instead of comedy, have a brief break from the monster. Like you know how the monster jumps to life when the character examines its body? Yeah, something like that. Everyone is all "We did it! We defeated the mons-" then they get cut off by said monster dropping down on them. Would that be scary? I don't know, I've never written or even read horror. I'm a scaredy-cat. I blame my overactive imagination.
