Comic relief

Comic relief is "the inclusion of a humorous character or scene or witty dialogue in an otherwise serious or dramatic work, often to relieve tension." The article glosses the mechanism as "a releasing of emotional or other tension by interposing a comic episode in the midst of serious or tragic elements," and the character version "often takes the form of, but is not limited to, a bumbling sidekick of the hero or villain," one who "will usually comment on the absurdity of the hero's situation." Shakespeare is the reference implementation: the Porter scene in Macbeth, staged just after Duncan's murder, and the grave-digger scene in Hamlet.

Placement is the craft: relief set beside the darkest beat lets the reader breathe and sharpens the darkness on return. The carrier is usually a sidekick or a trickster, and the joke timing itself is how to write comedy.