The Crusader Codex is given to every character when they are first made. It is a one of a kind item that cannot be un-equipped, cannot be sold, cannot be dropped, cannot be given potential, and cannot be traded. While hunting monsters around Maple World, they will have a chance of dropping a Monster Card when defeated. If you pick up that monster card, it will be added to your Crusader Codex automatically and you can then go and look up information about that monster whenever you wish.
As you collect more and more cards, you will start to fill up Monster Card Sets within the Codex. Each set can give the Codex bonus stats that will apply to your character, but only the bonuses of one set at a time may be used. As you complete a set, it will give your Codex some experience, and with enough experience your Codex can level up with your character, providing higher stat bonuses.
The other main function of the Crusader Codex is to store your monster familiar cards. Mobs have a rare chance to drop familiar cards upon dying, and if you pick these up, you can use them to add them to your Codex. You can them summon that Familiar at any time to fight alongside you and give you buffs. While Bosses do have familiar cards, it is currently unknown if the cards drop from the bosses or if they are only obtainable through Familiar Booster Pack in the Cash Shop.
Number of Upgrades
Cannot be sold
Only one of this equipment may be in a player's possession at a time.
Only one of this equipment can be equipped at a time.
The Crusader Codex is one of the most frequently broken parts of GMS
There was a memory buffer overflow error in 2015 that allowed players to gain massive, illegit stat boosts from their Crusader Codex. Some players were able to obtain 300+% Boss damage and total damage, and abused this glitch to take down bosses that they would otherwise be unable to fight
Not every codex set is currently available to obtain due to some areas of the game being removed or revamped after the codex was implemented in the game. However, they are all still listed in the Codex.
Although the Max level of the Codex is 10, currently in GMS there only exists enough Sets to get the Codex to a max level of 8