Please don't list this on a work's page as a trope. Examples can go on the work's YMMV tab.
Nightmare Fuel: Sonic Shuffle
One of the most frightening Mini-Events involves Medusa, who paralyzes your character for up to two turns if they don't have a Forcejewel to save them.
One Mini-Event has the character encountering a hooded ferryman, who asks them if they will steer the boat themselves. Depending on how they answer (and the mercy of the RNG), it can be Illumina, who helps the player◊, Eggman, who just thought he'd ask, or Void, who sends the player back where they started◊.
Another Mini-Event has a hooded priest◊ who asks if the time has come, and can be either Illumina, Eggman, or Void. Void in particular has a creepy◊ response◊.
The Mini-Game "The Grest Escape" involves everyone trapped in a building/maze, which Eggman is set to blow up if they don't escape.
One Accident Mini-Game in Nature Zone involves everyone having to escape from the mouth of a crocodile. If they fail to escape, they're eaten.
Void's monster form. Its head is its chest, and it shoots beams of darkness to capture the characters and drain their Rings.
Since Void is Lumina's opposite and part of Illumina, it's likely that Lumina and Illumina would have similarly scarring forms if they ever snapped.