Eldritch

• Blue, Red & Green book = main campaign. You can enter and leave these when you like, as long as you return to the entrance of the book.

• White book = Mountains of Madness. Basically a second, harder campaign. You can make it easier by playing parts of the main campaign first to stock up on items, artifacts, bullets and keys.

• Orange book = The Asylum. A challenge mode in which you collects souls. Note that the game doesn't end if the countdown reaches zero, it just spawns a demon.

• Halloween Pumpkin = Trick or Treat. A quick mode in which have to reach the exit before unkillable demons get to you.

• There can only be a limited amount of monsters in an area. This includes their corpses, which will stay around forever if you don't loot them, even if you exit the book!

• While doing the main campaign you may find Dusty Books. Using them will take you to a small area with a mysterious item. These are part of a challenge, you can ignore these items during your first playthrough.

• Lizardmen statues become active when you are close to them and enter their sight range. You will know, because there will be a sound and some sort of dust effect. At that point they will be locked on to you until you turn your back on them, at which point they will teleport and attack. You will stop them from being active by keeping a line of sight to the statue and side-strafing until walls block vision.

• The Destruction Amulet allows you to destroy terrain with the pistol, allowing you to dig around with bullets. The amulet also allows you to destroy locked wooden doors with your knife.

• Mountains of Madness introduced Climbing Boots as an item, but you might also find them in a shop during the main campaign. They prevent icicles from falling, which will be your main source of frustration in MoM.