These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Nightmare Fuel - In September 2010, Johto was blanketed by fog and Psychic- and Ghost-type Pokémon gathered. The result was lasting nightmares for anyone who fell asleep before the fog lifted. And some of them were downright awful.
And then there was the Missingno event around Halloween. Skeletal Aerodactyl and Kabutops running around with standard Missingno while the whole world and all NPCs turn pixelated? Brrr.