Sound Test Mode
When the second or third disk is inserted and the game is accessing the disk, keep the [SELECT] key pressed to enter Sound Test mode. This can even be done while playing the game. In sound test mode you can select a level with the up/down cursor keys and a sound clip with the left/right keys. Use [SHIFT] to play the selected clip. To exit Sound Test Mode, select song number 0.
Also while the game is paused, you can press [SELECT] to have the sprites animate, or you can keep [SELECT] pressed and use the cursor keys to adjust the screen position.
You can bypass the introduction and go straight to the game by starting with the second or third disk.
When starting with the third disk (DISK C) on the weapons select screen keep [SELECT] pressed, you can now use the cursor up/down keys to select the starting level.
Adjust ship speed
You can use the [STOP] key to pause the game, after which you can adjust the speed of your ship (LEVEL) with the left/right cursor keys. Press [STOP] again to resume.
By putting disk A instead of disk C in your machine when finishing level 4, you will get a demo.
Beat the game and keep SELECT pressed while loading the ending, then "true ending" is displayed. It describes the protagonist's father who supposedly died in the opening has survived riding a whale.