How about 2 endings: One where Link kills Zelda, and the other where he saves her from the darkness? The idea that had been thrown around for the Zelda battle was that you had to use the magic from light arrows to dispel the darkness surrounding Zelda. But, firing an arrow at her directly would hurt her. So, you had to shoot at one of the mirrors on the edges of the room, causing the arrow to fall away, and reflecting the light back at Zelda.
