Completing the game will not get you the 666 victims across the game that you need for this trophy so you will need to grind out a load of kills at the end.
The best level for this is Deleted Scene 3 from Slayaway Camp 2 because it has 4 victims and can be completed in 15 seconds if you skip the 4th kill animation.
Once you have completed the level you just re-enter it and do it again and again until the trophy pops because unlike normal scenes the deleted scenes don't run consecutively.
The solution to the level is as follows:
Up, Right, Down, Left, Up