1996 The Spooktacular New Adventures of Casper - Halloween

From Wikipedia: The Spooktacular New Adventures of Casper (also known as simply Casper) is an animated television spin-off of the 1995 feature film Casper, which, in turn, was based on the Harvey Comics character of Casper the Friendly Ghost. It aired on FOX Kids television and FOX Family Channel from 1996-1998 for 3 seasons, 52 episodes. Many of the same people who worked on this show also worked on Animaniacs and Pinky and the Brain.

The first segment is called:
Spooky & Poil Meet the Monsters
Responding to a Haunt Ad, Casper's mischief-minded cousin, Spooky (along with his "ghoulfriend" Poil in tow) investigates a creepy old house hoping to get a job haunting the joint. But they must contend with Frankenstein's monster, Dracula, the Wolfman, the Gill-man, the Mummy and the Invisible Man.


The second and third segments are called:
The Ghostly Trio
Edward-Gorey-esque rhymes and artwork, telling a tale of how Casper's uncles, the Ghostly Trio, decide to leave when everyone ignores them. Narrated by Kat, Casper's thirteen year old human companion.

AND

The Tricks a Treat
When Kat's school enemies, the rich spoiled Valley Girl-types, Amber and the Jennifers announce that they're having a big Halloween bash, Casper (disguised as a P.A. box) announces that Kat is also having one - with real ghosts. But as it turns out, it's against Spooksters Union rules for ghosts or monsters to scare on Halloween. With appearances by the Ghostly Trio, Dracula, Frankenstein's monster, the Mummy, the Wolfman and the Gill-man.