Red herrings
Who are some characters introduced for no other reason than to be a red herring? They have nothing to do with story or plot, and if they were removed it would make no difference to the story, but were there to make the audience think for a second they were the killer.
Scream 2: the two soroity girls played by Rebecca Gayheart and Portia de Rossi. After Sid is attacked at their soroity party (after Cici is killed), the two of them are standing outside where GF escaped. It seemed, at the time, they were meant to be suspects for a hot second.