These need to be entered in-game, not at 'redeem code' on xbl marketplace.
Spooky Mechromancer Skin in Borderlands 2: WTKTJ-696S5-R9RB6-5RTT3-BTS3H
Spooky Zer0 Skin in Borderlands 2: 5J53B-J96HW-F9FBX-CFTT3-FTFXS
Spooky Axton Skin in Borderlands 2: KBKBT-WH6Z5-X96B6-WX3TJ-5J6J3
Spooky Salvador...