The best horror-comedy still makes a genuine effort to scare you
There’s a scene in Krampus that encapsulates this. If you’ve watched the film, you know exactly which scene and character I’m referring to. It’s the only scene from that film I actually remember.
A better example (and overall better film) is An American Werewolf in London. Filled to the brim with iconic black comedy, but tue werewolf scenes themselves are always taken seriously. Landis is very careful not to over-inject those comedy elements into the transformation scene.