Some Scooby-Doo villains were clever. Some were memorable. And some were simply terrifying.

In our last Mystery Machine Lore deep dive, we looked at the greatest villains Scooby-Doo ever created. This time, we're asking a different question: which monsters were actually the scariest?

The Scariest Scooby-Doo Monsters Ever Created explores the creatures, ghosts and supernatural threats that pushed Scooby-Doo closest to genuine horror. From unforgettable monsters of the original series to darker threats from later shows and movies, we're looking at what made these creatures work — their appearance, atmosphere, behaviour, sound, story and the sheer fear they created whenever Scooby and Shaggy encountered them.

Some were criminals hiding behind masks. Others blurred the line between elaborate hoax and genuine supernatural horror. And a few made Scooby and Shaggy's instinct to run away seem entirely reasonable.

Across more than five decades of Scooby-Doo, these are the monsters that left the biggest nightmares behind