Puck the Elf mini-game
Successfully complete the game under the easy difficulty setting.
Battle arena mode
Successfully complete the game under the normal difficulty setting.
No limit mode
Successfully complete the game under the very hard difficulty setting.
Easy hard mode prizes
Use the following trick when obtaining the hard mode prizes. Set the difficulty to easy and proceed to the final stage save point (before fighting Balzac's first form). Quit and save the game. Set the difficulty back to hard and continue the game. Even though you completed most of the game under the easy difficulty setting, you will still get the prizes for hard mode. You still have to complete the final stage in hard mode, but some tough sections (such as the battle with Zod) are a lot easier.
Front and rear attack
Fire the hand cannon while your sword is drawn. As you are firing, keep pressing X (main sword attack). After the cannon blast fires and knocks Guts back, he will spin and slash his sword behind him, defeating enemies to the rear.