Dark Link will mimic your moves at first, doing exactly what you do, but dodging any attacks towards him. He will stand on your sword if you thrust it at him and may attack depending on his form at the time. You have to attack him with your sword once at the very beginning of the fight for the advantage. The easiest way to defeat him if with the Megaton hammer since he cannot block or mimic this way of attack, which the Biggoron's Sword and Giant's knife are also useful as Dark Link cannot block these attacks easily, but using these weapons is also taking a chance as you cannot shield yourself while using these weapons, so the best option is using the Master Sword the whole time in strikes of three at a time while Z-targeting Dark Link since the third attack will always differ from the first two and thus, strike Dark Link, but Dark Link can easily counter most sword attacks. Dark Link will be transparent for a while and will not attack, but block any attacks. You can also use the Hookshot as well, which he will dodge, but will leave him then vulnerable for a few seconds that you can use to quickly attack. Once injured after a while, he will attack on his own. Dark Link has exactly the same health as Link at the time of the battle. If Dark Link is struck while Link is near the island in the center of the room Dark Link will reappear behind him, but if Link is at the edges of the room, Dark Link will be back at the island. A very easy way to defeat him is with Din's Fire since it is unblockable, thus Dark Link cannot defend himself from this attack. Dark Link's voice is deeper than Link's, and when defeated, he drops through the shallow waters of the floor with a scream and leaves behind 15-20 rupees. Afterward, the scene disappears to reveal a different room and you can then obtain the Longshot. Having said that, I believe Dark Link is a good guy placed in that room by King Zora to protect the Longshot, which is a bit like the Zora's treasure in the Water Temple. If you ever have any questions referring to Dark Link, I'll be glad to answer them!
