Looking for a horror movie
10 or 15 years ago I saw a movie on tv.
What I remember is: its a horor/slasher or horror/comedy from the 80's
Its about some students at a school, I remember a scene where the students are dressed in costumes to a halloween party or something like that at the school, and the killer is going around killing the students meanwhile the other students just think its a prank and think its one of the students because he is known to do pranks what you also see through the movie.
I know its not Killer Party, April Fools day, terror train, Slaughter High, Return to Horror High, Student Bodies
Anybody knowns?