If you are having a hard time defeating the two dark knights in hyrule castle's beginning, follow this tip:

1. Make sure you are standing near the beginning door with out them walking toward you.
2. Shoot an arrow at the one on the right (for some reason, if you shoot the one on the left they both come)
3. Wait for it to come to you.
4. When it's at you, defeat it once. Don't get too close to the other one while you fight.
5. Defeat the remaining dark knight.