Here is the full list of all 50 Slayaway Camp achievements. It takes around 15-20 hours to unlock all of the achievements on Windows.
Unlock 5 Killers using the Mystery Box.
Unlock 13 Killers using the Mystery Box.
Kill 666 victims across all Slayaway Camp movies.
Unlock the gorepack called Puffed Up.
Complete Slayaway Camp X "Space Camp"
Unlock the gorepack called Face Stapled.
Unlock the gorepack called Charbroiled.
Unlock the gorepack called Party's Over.
Get a score of 20 in Faces of Killed 3.
Complete Slayaway Camp 8 "Manhattan Manslaughter"
Unlock the gorepack called Cinco de Slayo.
Unlock the gorepack called Demonized.
Unlock 13 Gore Packs.
Unlock the gorepack called Origami'd.
Complete Slayaway Camp 7 "Office Hours"
Unlock the gorepack called Juiced.
Kill a victim by scaring them into an electric fence.
Complete Slayaway Camp 6 "Fatality Ward"
Unlock the gorepack called Broken Heart.
Unlock the gorepack called Spronged.
Unlock the gorepack called Pincusioned.
Unlock the gorepack called Double Blind.
Use the Mystery Box once.
Kill a victim when the lights are off.
Complete Slayaway Camp 5 "Bloodbath Beach".
Kill a swat cop.
Unlock the gorepack called Pruned.
Kill 30 dumb cops across all Slayaway Camp movies.
Complete Slayaway Camp 4 "Slash'em High".
Complete Slayaway Camp 3D "The Abusement Park"
Unlock the gorepack called C-flat Face.
Unlock the gorepack called Ball'd Faced Lier.
Kill 100 victims across all Slayaway Camp movies.
Get through a level with a cat without killing it.
Kill a victim with a Landmine.
Unlock the gorepack called Grenade!.
Get a score of 13 in Faces of Killed 3.
Get a score of 10 in Faces of Killed 3.
Get a score of 5 in Faces of Killed 3.
Complete Slayaway Camp 2.5 "Another Return to Slayaway Camp".
Unlock the gorepack called Not the Bees.
Complete Slayaway Camp 2 "Return to Slayaway Camp".
Kill a victim by knocking over a fridge onto them.
Kill a victim by scarin them into water.
Kill a dumb cop.
Unlock 1 Gore Pack.
Complete Slayaway Camp.
Kill a victim by scaring them into a hole.
Kill a victim by scaring them into a fire.
Get a score of 25 in Faces of Killed 3.