Code3breaker being the most difficult codes in Geometry Dash is in the Vault of Secrets. The Vault of Secrets can be unlocked by getting 5 demon keys which you can get by collecting 500 mana orbs. (Every 500 mana orbs you get, you get a demon key.)
You will type Cod3breaker in the text box above the Vault keepers face.
You will see a bunch of numbers pop up on the screen. (There should always be six numbers and they are always completely random. The number that comes next will always be bigger than the previous number.)
You will sort them from first to last in (A-F, "A" Being the first and "F" being the last, and "X being undefined. You will solve for "X" later in the tutorial.)
Example: 12, 34, 67, 87, 121, 151.
A = 12
B = 34
C = 67
D = 87
E = 121
F = 151
Then you will do some mathematics and solve for the unknown:
B - A = X
C - B = X
D - C = X
E - D = X
F - E = X
Then solve for the unknown:
34 - 12 = 22
67 - 34 = 33
87 - 67 = 20
121 - 87 = 34
151 - 121 = 30
Then you will put them all in the code (Don't add the numbers!):
XXXXX
2233202430.
I hope this Tutorial helped you!