This only works in the original North American version of the game. It may not work in other versions.

Complete the game in all 8 save files (save at the last possible point). Once you have a completed game in every save file, start a new game overwriting the first game file you have. In this new game you will have the Lightsaber, or "Queen's Sword" from the start of the game.

This works in the original PAL and Japanese versions of the game. It may not work in other versions.

Beat the game and wait for the credits to finish. Once you gain control again, search for Yorda along the shore. You should now see the real ending and get a chance to save. Save and restart the game. Yorda should be a controllable second player. Make your way through the game to [[The Waterfall]]. Play until you get the mace by throwing a ball in a box. Instead of a mace you'll get the Lightsaber! It kills shadows in 1 or 2 hits.