Santa Claus remains terrifying until children are about 3 years old.
Madness string 7564
It's a tentacled mass of ever-changing proto-flesh and temporary mouths screaming the song of Ragnarok, except for the ninth mouth, which is forever stitched up with the stolen sinews of Zeus.
There's a theory that you can cure this by following standards, except there are more 'standards' than there are things computers can actually do.