This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / Shrek the Third
The dream that Shrek has after he "wakes up" from his other dream.
IT HAD A BABY HEAD ON A DONKEY'S BODY!
The DVD menus, especially the main menu. A bunch of curtains open, a bunch of fake clouds descend on THOUSANDS of strings (looking eerily like marionettes), and all you see is the blank, gloomy-looking, huge andnot quite real-looking stage where Charming's play takes place. No characters, no voiceovers, just that enormous and clearly artificial stage, engulfed in darkness, with sinister music playing in the background. The submenus (for extras, language selection, etc.) sort of subvert this by having some of the main characters present, but the huge menu titles meant to look like suspended stage props are still kinda creepy.
If Prince Charming's sword had landed just a little bit to the left or right, he would have succeeded in killing Shrek.