The 1974 AIP film Madhouse stars Vincent Price and Peter Cushing, with the "participation" of Boris Karloff and Basil Rathbone, even though by 1974 both of them had been dead for years. That "participation" is just clips from some of their films, as Price's character is a horror movie actor famous for playing a madman, who goes....MAD! You can watch it on the thisTV channel (!?) at 5pm.
In the meantime, can you take the trailer? CAN YOU?