Karateka (Commodore 64)

Anti-Piracy Features
The game has multiple routines related to copy protection, taking a minefield approach to anti-piracy:
 * 1) A routine that checks one byte, which scrambles music.
 * 2) A routine that checks one byte, which makes playing by the keyboard impossible.
 * 3) A routine that prevents the player from walking through a door.
 * 4) A routine that increases the opponent's regeneration.
 * 5) A routine that makes the hawk invulnerable.
 * 6) A routine that prevents movement when facing the final opponent.
 * 7) A routine that crashes the game when played on an NTSC system.
 * 8) A second routine that prevents walking through a door.
 * 9) A routine that is active before the game loads the levels.