Just when you thought you'd seen all a game had to offer, in comes something out of your worst nightmares to give you the heart attack of your life.
A video game without secrets is like a Celebrations tin without those Maltesers ones that everyone fights over. You may have had the story mode done and dusted ages ago, but does that mean the game is over? More often than not, hell no!
Of course there's still more to see. Whether it's side missions, collectables or just another playstyle you haven't tried out yet, you'll likely be playing for countless more hours before you finally decide you haven't left a single stone unturned.
But I'm betting you have...
These well-hidden horrors are as eerie as they are elusive. Even when they don't pose a threat to your character, just seeing them alone is enough to rattle you for the rest of the night. And the fact they've been there all along, slipping past you no matter how many times you've played the game and claimed to have explored its every orifice, only makes it that much creepier.
10. Starro The Conqueror - Batman: Arkham Knight (2015)
The largest of Batman: Arkham Knights DLC expansions, A Matter of Family, is set on an oil rig way out to sea that was converted into a theme park and then abandoned. Is that not creepy enough?!
You'll find the answer to that one only if you're the most thorough of explorers. An extremely hard-to-see grate underneath the locked central building takes you into a secret room, pitch black save for two glass tanks in the far wall. And in one of these tanks is something you never expected to find in a million years: the mind-controlling alien, Starro.
Pressed right up against the glass, his one giant eye appears to follow you, and if you listen closely, a wheezing, static-like sound can be heard, which may or may not be a result of his psychic abilities.
Detective Vision give you a slightly better look at his unsettling form, but otherwise, the classic DC foe is just there to creep you the hell out.
And creep us out, it did.