Summary
The Itempedia of The Nightmare is a hidden category separate from the Frontier's Itempedia. It can only be viewed after the players have entered the hidden room in The Deli and pressed the orange button, in order to access The Hidden Library. It is located in the Entrance Hall, where a door with an orange hexagon-like eye above it can be found after a small set of steps.
Unlike the Frontier's Itempedia, the Itempedia of the Nightmare houses many collectibles from different categories of the game, from consumables to monster drops, from plant to garments. Most of the skills learned from all four sections of the Frontier's Itempedia are required to fulfill the completion of it.
Completing the Itempedia of the Nightmare allows the player to get the Falling Light Set from the purple door room in The Hidden Library.
List of Known Collectibles
There are currently 72 collectibles in total that are categorized under the Itempedia of the Nightmare. This table will be sorted in the order it goes in.