Clay Doll Outfit
- Location: Shrine of the Frost Giants (D-1) - Defeat Balor.
- Usage: Goes through the deadly purple lasers throughout the game. Immunity to poison gas, lava, poison lava, the life-drain ability of various enemies (such as the Basilisk) and the deadly vacuum of space. While equipped, you move slightly slower, unable to double jump with the Feather and you jump slightly lower. Your Main attack is replaced with a powerful punch while your sub weapon attack is replaced with firing a beam.
- Location: Icefire Treetop (F-3)
- Break left wall; Open with Skeleton Key.
- Location: Immortal Battlefield (H-5)
- Enter the Cavern to the right of (H-3); Open with Skeleton Key.
- Location: Gate of the Dead (D-4)
- Break the wall on the bottom-left of the room (when the gravity door is on the rightside-up); Open with Skeleton Key.
Eastern European Outfit
- Location: Ancient Chaos (C-3) Corridor of Blood entrance.
- Whip the left wall to reveal it; Open with Skeleton Key.
Kickstarter backers received up to 4 keys upon release with the number being determined by their pledge level. However, the keys are also obtainable for non-backers via completing achievements:
- Everyone Has Their Reasons: Visit Nebur's store 40 times (triggers a new message after the 20th visit and triggers an achievement when completed)
- Treasure Hunter: Getting all items (Ankh Jewel not required)
- Moment of Release: Clearing the game
- Encyclopedia Completionist: Completing the glossary (Entry 19 in Main Characters isn't required apparently)
Any unused key is indicated by a key icon on the Main Menu, right above System Controls, and going back to Main Menu is vital to trigger the costume chests. The keys are available the same way in the Playism version, you just won't get an achievement notification.
6th Costume Mystery
One of the slots is unused even on a 100% game, if anyone finds anything about it please report back the findings.