This code applies to any non-US version of the game only.
With 2 Player Mode enabled, play the game through the waterfall and reach an area where you get the mace by throwing a ball into a box at the first play (Please refer to FAQ for this side quest). This time a Starwars-like Weapon will fly in instead of mace.
This weapon is very powerful and will kill the shadow within 1-2 hits. And the weapon will be prolonged to triple the size of the sword if you grabbed Yorda's hand when attacking. (Even longer than the original Star Wars lightsaber)