Courage the Cowardly Dog

This Cartoon Network classic is easily one of the creepiest shows ever made for kid. Courage the dog lives in the middle of nowhere with his elderly owners, Muriel and Eustice Bagge, who are blissfully ignorant to all the supernatural stuff that occurs on a daily basis. Superbly animated with excellent expressions, you can't help but sympathize wit Courage. Maybe he has a point, being so scared all the time.

The Grim Adventures of Billy and Mandy

After challenging the Grim Reaper to a limbo contest and winning, the Grim is bound by his word to be the friends of Billy and Mandy. Billy is the village idiot, while Mandy is a deadpan kid with a dark sense of humor. The comedy of this show is totally priceless-- it definitely stands the test of time. The aesthetic is super neat and the episodes are genuinely entertaining. Watch My Fair Mandy, the episode where Mandy smiles. The ending is HILARIOUS!

Scooby-Doo, Where Are You!

A classic, does this show even need an introduction? Scooby-Doo, Where Are You! follows Scooby-Doo and friends as they travel to different towns and solve mysteries about supernatural beings haunting or scaring people. The gang taking on costume-wearing weirdos harassing little towns really makes the month of October worth living. Any episode is great if you just want some supernatural mysteries to be solved, with the classic Mystery Incorporated's hijinks and aesthetic.

Danny Phantom

This truly ICONIC show really was the blueprint. Though it's not terrifying or anything, the style was super cool, and each ghost was so creative with sick background stories. The special episodes are also pretty entertaining! It's easy to understand why Danny Phantom was such a popular show during and after it was aired on Nickelodeon. The show follows Danny Fenton, a high school freshman who is half-ghost, as he uses his supernatural ghost powers to fight other ghosts that wreak havoc in his town.

Martin Mysteries

Martin Mystery is a Canadian cartoon based on the Italian comic, Alfredo Castelli's Martin Mystère. This was during the weird period where western shows were experimenting with borderline anime-style. The series follows Martin, Diana, and Java, agents of "The Center," an organization tasked with ridding the world of supernatural beings. The animation is definitely fairly creepy at times-- this show is like if you combined totally spies with Goosebumps.

Invader Zim

Invader Zim isn't technically supernatural, but it's color scheme and animation style definitely make it an October classic. The show follows Zim, an alien tasked with destroying the planet, as he plots everyday to achieve the annihilation of the human race. If only it weren't for Dib, the only human that figured out Zim's identity, who keeps thwarting Zim's plans.

Tutenstein

When a bolt of lightning resurrects King Tut, who becomes a teenage Frankenstein-Mummy living in the 21st century with his new human friend Cleo, and cat Luxor. Just because he's technically 3000 years old doesn't mean Tut acts any less like a spoiled, teenage boy. Tutenstein follows the everyday adventures of Tut as he adjusts to the world and deals with everyday troubles as well as supernatural ones.

Edgar and Ellen

Edgar and Ellen is a TV show based on the children's books series. It follows orphans Edgar and Ellen, who are two mad scientist, evil kids that cause mischief in their town. These kids are literally grey, looking like creepy little Tim Burton characters in a bright, colorful town full of nice people. Ellen, the older twin, specializes in plants and fauna, while Edgar is more of an inventor/scientist, but both are ingenious kids that use their intellect for evil. The evil characters and locations in this show are pretty creepy, but the cute little town balances it out.