Play the game, get a high score and get a game over. Do this five times. At the name entry screen input the same name all 5 times. When the hi-score list is populated by the same name, the game will be in hard mode.
Note: This trick requires two controllers. Perform the following steps for double firepower:
1. Connect the 5-player turbo tap 2. Plug a single controller into port two 3. Turn on the system 4. Choose a two-player game 5. When the game starts, pause it and remove the 5-player turbo pad 6. Plug a single pad or joystick into the system 7. Unpause and try overlapping the two ships