* EarWorm: The animated series is chock full of these. [[https://www.youtube.com/watch?v=mMEYl3nLSS8 The intro]] is only the tip of the iceberg.
* NightmareFuel: It's not a particularly scary book in the traditional sense; Harold is a little boy who draws things with his crayon and they come to life, and they're almost exclusively nice things. The creepiness [[FridgeHorror comes later]] when you realize that Harold is the ''only'' real character in the book. The whole world is empty, except for Harold and his crayon.
** Averted in the animated series which starts and ends in the Harold's room, with an art shift to make it clear what happens in Harold's imagination and what happens in the real world.[[note]]things happening in Harold's imagination has a purplish tint as it is drawn using the purple crayon.[[/note]] Also, Harold's parents are often mentioned and his mom ([[TheFaceless although only her hand is visible to the audience]]) appears at the start of the several episodes to [[{{Jossed}} joss]] the fact that Harold's alone in the world.
* RecursiveAdaptation: The HBO series actually spawned several baby books.
%%* ThatRemindsMeOfASong: The animated series is ''very'' musical and breaks into {{Disney Acid Sequence}}s very frequently, more than once an episode.
* SweetDreamsFuel: Pretty much the whole HBO show, except for...
* TearJerker: "I Remember Goldie". Harold's goldfish passes away, and he meets a mermaid who tells him death is a natural part of our life. *sniff*