4th wall clues

This topic refers to clues that are only noticeable by player, and not necessarily character in the game. They may require the player to read documents,

Via documentation or boxes

 * KQ6 comes with a Guidebook to the Land of the Green Isles for the player to read, and also offers clues to solving several puzzles (as a form of copy-protection). Alexander is able to solve these puzzles without actually 'having a copy' of the book on his person. The Companion subverts this by saying that he had a copy of the guidebook before he came to the Green Isles and memorized it, though he had lost the copy when his ship went down.
 * John Williams mentioned in an InterAction article that sometimes the boxes contain clues. For example in KQ2 you can see a picture of Pegasus where the snake is located in the game, which might offer a clue to vigilant players that not everything is what it seems, and try something they might not have thought of on their own.

Via cutscenes
This refers to clues only seen via cutscenes, that the character would not actually see themselves.
 * In KQ6 if the player is paying attention to the cutscenes between Abdul Alhazred and Shamir in the wizard's office they will notice what genie's bottle looks like. Even if Alexander is not there himself. This is subverted in the novel, as Alexander actually visits Abdul's office when speaking to the wizard, and see's the bottle there.

By Death
These are clues that only noticeably by first being killed and require the player to reload. Save early and save often.
 * If Graham is captured by the innkeepers in KQ5, if the player is paying attention they might have noticed an inconspicuous rat hole just behind the tied rope where Graham is left, before the death message pops up.
 * Trying to open the bottle in KQ5 shows you what the bottle is capable of doing, in the process of leading to a death scene, which can offer a clue to what it could be used for if only to trap someone else.
 * Dieing any time in KQ6, shows a cutscene of Alexander being taken to the Land of the Dead and giving a ticket to the gatekeepers. This offers a clue to a future event.