Instructions
Cast Din's Fire. This is the only magical attack that Dark Link cannot block. Try to back him up against a wall before using Din's Fire, otherwise he will dodge the attack. You can also lure him into a corner with your back facing him, and then unleash the magic. Keep your Green and Red Potions close at hand if you try this technique, as your Magic Meter will deplete quickly.
Use the Master Sword. Because Dark Link can block or dodge most other techniques, it might be wise to stick with regular sword attacks. Avoid targeting Dark Link, as he will be more likely to anticipate your swings while targeted. Opt for a slow, steady sword fight if you're low on health, using the Hylian Shield to block Dark Link's strikes. A quick, all-out sword assault will work as well, but you'll likely take substantial damage.
Try the Megaton Hammer. You can deal large amounts of damage to Dark Link with this method, but you'll have to time your movements wisely. Wait for an opening in Dark Link's defenses before you attack. Press "A" after the swing to equip the Hylian Shield and block Dark Link's incoming attack. Be quick when switching between the two items, as you will be leaving yourself open to damage.
Stun Dark Link with Deku Nuts. To prevent Dark Link from adapting to this tactic, keep your back to him when he's at a distance. This will lure him in closer. Throw the Deku Nut when Dark Link is in range, and then move in for a sword attack while he's stunned.