Greg Eagles
Grim (voice) (184 eps)
Richard Steven Horvitz
Billy (voice) (184 eps)
Grey DeLisle
Mandy (voice) (184 eps)
Vanessa Marshall
Irwin (voice) (184 eps)
Rachael MacFarlane
Mindy (10 eps)
Diedrich Bader
Hoss Delgado (voice) (6 eps)
Dee Bradley Baker
Mandy's Dad (6 eps)
Phil LaMarr
Hector Con Carne (6 eps)
Maxwell Atoms
Jeff the Spider (voice) (6 eps)
Candi Milo
Grim's Mom (voice) (6 eps)
Armin Shimerman
General Skarr (5 eps)
Jake Thomas
Nigel Planter (4 eps)
Jennifer Hale
Gladys (voice) (3 eps)
Martin Jarvis
Nergal (3 eps)
John Vernon
Dean Toadblatt (3 eps)
Frank Welker
Scooby-Doo (voice) (2 eps)
Jane Carr
Pud'n (2 eps)
Henry Gibson
Lord Pain (2 eps)
'Weird Al' Yankovic
Squid Hat (2 eps)
C.H. Greenblatt
Fred Fredburger (voice) (2 eps)
Debi Derryberry
Nergal Jr. (2 eps)
Tom Kane
Professor Utonium (2 eps)
John Kassir
Lord Moldybutt (2 eps)
Jeannie Elias
Malaria (1 eps)
Alan Oppenheimer
Father Time (1 eps)
Keone Young
Kwan Ti (1 eps)
Wayne Knight
Jack O'Lantern (1 eps)
Scott Menville
Pinocchio (1 eps)
Mary Jo Catlett
Witch (1 eps)
Fred Willard
Boogey (1 eps)
Rob Paulsen
Tooth Fairy (1 eps)
James Arnold Taylor
Fred Flintstone (1 eps)
Nika Futterman
Pandora (1 eps)
Ronnie Schell
Dean Toadblatt (1 eps)
Laraine Newman
Crossing Guard (voice) (1 eps)
Cree Summer
Cave Witch (voice) (1 eps)
R. Lee Ermey
Sergeant / Drill Sergeant (1 eps)
Michael Dorn
King Beardbottom / Clown / Dwarf #2 (1 eps)
Jennifer Darling
Pollywinkle (voice) (1 eps)
Malcolm McDowell
Baron Von Ghoulish (1 eps)
Carol Kane
Mrs. Claus (1 eps)
Gilbert Gottfried
Santa Claus (1 eps)