Castelian (NES)

Secret Message
At the Game Over screen, press and hold A + Select + Up on Controller 1, then wait until the title screen re-appears. Instead you'll see the secret copyright message. The message itself is encrypted by xoring with value, and can't be found in hex editor as a plain text.

Disabled Cheats
A couple of disabled test cheats still linger, and can be re-enabled with the following Game Genie codes.
 * (US version) or (Japanese version) – Enables an invincibility cheat when you press Down + Left + A + B simultaneously. Also, if you enter a door, the level will be automatically finished.
 * (US version) or (Japanese version) – Automatically finishes the level right then and there when you press Down + Left + A + B. Use with the above code, or it won't work for some reason.

Antipiracy Check
The US version of this game have some sort of protection from changing it's data. During entering the level, the game performs full PRG BANK 3 (contains most of in-game texts, as well as hidden copyright message display routine) data xoring and verify the result, if it is wrong, the code will jump to the wrong location and hang. The Japanese version still have the same test routine, but it never used.

Source Code
A fragment of uncompiled code is stored in the ROM at address :