Suggestions by @mr_blue_sky

Jerry Lewis

as The Klowns in If Scooby-Doo! had slasher icons

Paul Frees

as Billy Loomis in If Scooby-Doo! had slasher icons

June Foray

as Annabelle in If Scooby-Doo! had slasher icons

Alan Oppenheimer

as Harry Warden in If Scooby-Doo! had slasher icons

John Erwin

as Jason Voorhees in If Scooby-Doo! had slasher icons

Josh Brolin

as Conductor Ben Carne in Terror Train

Emma Bading

as Alana Maxwell in Terror Train

Paul Frees

as Jason Voorhees in If Scooby-Doo! had slasher icons

Morgan Freeman

as Prince Mamuwalde in If Scooby-Doo! had slasher icons

Kane Hodder

as Jason Voorhees in Nightmare 13: Freddy Meets Jason

Robert Englund

as Freddy Krueger in Nightmare 13: Freddy Meets Jason

Howie Mandel

as Gizmo in If Scooby-Doo! had slasher icons

Henry Gibson

as Chop Top Sawyer in If Scooby-Doo! had slasher icons

Norman Alden

as Ghostface in If Scooby-Doo! had slasher icons

Bruce Campbell

as Ash Williams in If Scooby-Doo! had slasher icons

Cassandra Peterson

as Elvira in If Scooby-Doo! had slasher icons

George O'Hanlon

as Norman Bates in If Scooby-Doo! had slasher icons

Roddy McDowall

as Herbert West in If Scooby-Doo! had slasher icons

Michael Bell

as Freddy Krueger in If Scooby-Doo! had slasher icons

Don Adams

as Chucky in If Scooby-Doo! had slasher icons