Garfield's Halloween Adventure quickly turns from a comedy to a creepy ghost story set in an abandoned mansion told by a creepy old man, which turns out to be true. Making it worse is how the old man is animated more eerily-realistic than any other human in the special.
Old Man: The pirates had a 10-year old cabin boy... I was that boy. I never took the treasure, because they would have found me! There's no escaping them! They know we're here, they know who we are!!
The old man mysteriously disappears when Garfield looks away for a moment to look at the clock in the mansion. He stole the only boat leading to the island, leaving Odie and Garfield stranded just as the clock strikes midnight and the pirate ghosts arrive...
The clock strikes midnight, then everything goes completely quiet. Garfield thinks the old man's story was just made up. Then a ghostly light appears in the fog over the water...
The Scare Chord when those pirate ghosts come through the cabinet will make you jump, especially right after Garfield says, "Maybe they didn't see us..."
The terrifying shot of the ghosts chasing Garfield and Odie down the pier, essentially forcing them to jump into the water to get away—only Garfield can't swim.
Even the part at the end of "Scaredy Cat" qualifies, what with the gradual build-up, the singer's tone of voice (and Last Verse Slowdown), and The Reveal, at which Garfield and Odie both scream like little girls. During this time, each and every time, the music speeds up.
Also of note, when Garfield tries to prove how brave he is by revealing all of the neighborhood children behind their masks/in their costumes, the first ghost has werewolf feet underneath, the goblin masked trick-or-treater is an actual goblin and the second ghost has nothing underneath its "costume", and unlike the two ghosts, who were left confused by the boys getting scared, the goblin actually tries to grab Garfield and Odie as they run away!
The Mind Screw ending, where Garfield and Odie arrive home safely, having found their candy, and Garfield settles down to watch some TV before bed only to see the old man from the island somehow hosting an all-night pirate movie marathon. At this point, Garfield gives up and goes to bed.
"Unreal Estate," an episode of the TV show, which is just a compressed version of Halloween Adventure, featuring Jon, Odie, and Garfield moving to a creepy mountain house where the stories of hauntings are Real After All.
Garfield in the Rough, with the killer panther. What's scary about this foe is that the panther has a more realistic look to demonstrate how dangerous it is. Doesn't stop Garfield from attacking it when it threatens his family, though.
Before the panther loses consciousness from the tranquilizer dart, it raises its claw towards Garfield, ready to tear his belly open, and as it faints, it reaches out and touches him. The tabby cat is shown to be really scared, and it's clear to him that he has no chance to defeat the panther due to the great size difference between them. Good thing the rangers intervened just in time or Garfield would have been killed.
note of Garfield: His 9 Lives is about a "guinea pig" cat in a secret lab. If you don't get scared during the escape... you will during the Painful Transformation.