Monster Madness

This is by far the hardest achievement in the game. In order to get this achievement you will need to do the following to get the costumes.

ANDY
-Beat the game on childsplay
-Obtain all level 2 weapons
-Unlock every beastdiary entry
-Unlock all level 3 weapons

Zach
-Beat the game on thriller
-Obtain all level 2 weapons
-Obtain all level 3 weapons
-Collect all melee weapons

Carrie
-Beat the game on horror
-Obtain all level 2 weapons
-Obtain all level 3 weapons
-Collect all melee weapons

Jennifer
-S rank all levels on madness
-Obtain all level 2 weapons
-Obtain all level 3 weapons
-Collect all Melee weapons