What about unreliable narrators? A funny, unreliable narrator can be a fantastic vehicle for this balance. They might describe horrific events with a glib, humorous tone, forcing the reader to read between the lines to grasp the true terror. Or, conversely, a narrator trying to be serious might inadvertently reveal funny details through their biased perspective. The gap between the narrator's voice and the actual events creates a space where both horror and comedy can live.
The reader is doing the work of balancing the tones themselves, which is deeply engaging. Is the narrator making jokes because they're traumatized? Are they downplaying something truly awful? The humor becomes a symptom of the horror, and the horror is amplified by the narrator's attempts to deflect with comedy. It's a psychologically complex way to achieve the blend, and it can make for a fantastically unsettling read where you're never quite sure how to feel—which is the point.