Some levels in Castle Crashers can be bypassed while a player is in a cooperative game with another player who already has beaten that level.
A player may notice that, after exiting a game and reloading it, some levels will remain locked, even after completion. This is noticeable as early as the Forest Entrance level. To unlock this level permanently, Thieves' Forest must be completed. If playing with someone who has already completed Thieves' Forest, the player only needs to complete this level to unlock Forest Entrance, demonstrating that some levels can be skipped, as long as the one following it is completed. This means players can complete the game for a character, Skull, or for Insane Mode relatively quickly.
List of Mandatory Levels
If playing with someone who's completed every level, the following levels are required:
- Castle Keep
- Barbarian Boss
- Thieves' Forest
- Pipistrello's Cave
- Cyclops' Fortress
- Lava World
- Industrial Castle
- Dock (Your own character must have the 3 relics beforehand to count level completion)
- Pirate Ship
- Desert Chase
- Sand Castle Roof
- Corn Boss
- Medusa's Lair
- Full Moon
- Ice Castle
- Final Battle (You may exit to map as soon as you see the credits)
- You must quit to the Main Menu, start the game again, and defeat the final boss a second time or else your skull and/or character will not be unlocked. The first time you beat him unlocks the level, the second time the skull and/or character.
- If you skip any level on this list then you will not unlock your respective skull and/or character.
- Not every character unlocks another character when you beat the game with them. Because of this, it's recommended that you beat the game with characters that unlock another character first, then move on to the characters with no unlocks.
- By using this technique, you'll only play 16 of the 36 levels. That's only 44% of the levels, meaning that 56% of the game is just filler.