- Sonic the Hedgehog 2 contains data for a cut level called “Genocide City”
- Obscure Wolfenstein clone Corridor 7 randomly jumpscares the player with a red demon face during regular gameplay
- Dog Island, a Wii game in which all the characters are adorable chibi dogs, has a subplot about a doctor whose botched treatment caused the death of someone he loved many years ago. He still sees her in his dreams, unable to let go or move on.
I have an example of the opposite. In Cultist Simulator, a card game about summoning eldritch horrors and bringing about the next phase of the world, there are occult paintings you can make that represent a significant power in their principle. The Secret Histories painting is cut from the main game, but you can spawn it using the console. It depicts in a really silly art style two lovers significant to the principle kissing.