Shadow Link

Shadow Link is another form of Link, which is a reflection created by the Dark Mirror in that appears in The Legend of Zelda: Four Swords Adventures, and The Legend of Zelda: A Link Between Worlds. He is not to be confused with Dark Link, who is actually a separate character.

Appearance
Shadow Link has only a small amount of features similar to Dark Link. However, he has some very noticeable differences, including those above.

Four Swords Manga
In The Legend of Zelda: Four Swords manga, Shadow Link was drawn from the Dark Mirror by Ganon to act out his wishes. Shadow Link is a twisted version of Link, born from his own shadow, and is a cruel, malevolent and calculating character. He first appears after causing the Shrine Maidens to vanish, and proclaims himself to be "the hero, Link". Completely avoiding Link's attack, he immediately kidnaps Zelda and sends Link to the Four Sword Sanctuary, from which he observes as Link awakens Vaati. His next move is to lead Vaati's troops to attack Hyrule Castle and send all the Knights of Hyrule to the Dark World. There, he confronts the four Links, revealing himself to be much stronger than they are with their tainted blades, and striking them down with Sword Beams. They are saved by the Blue Maiden, who releases a Fairy to shine light upon him, stunning him long enough for them to escape.

Shadow Link continues to plot, hidden away from the light. As he cannot go out in daylight, he works with Vaati's minions to thwart the progress of the four Links. Using dark magic, he manages to split the four Links apart by sending them to four different lands of Hyrule, thus weakening the strength of the Four Sword. Then, confronting Vio, he attempts to coerce him into joining the side of darkness by appealing to his intelligence. Working with Vio, he traps Red and Blue in the Temple of Darkness, and allows Vio to be placed in charge of the Tower of Flames on Death Mountain. Vio even appears to kill Green in battle, totally convincing Shadow Link that he has turned to the side of evil.

However, Vio is simply putting on a show to gain his trust. Once inside, he learns about Ganon and his potential weakness, and the existence of the Dark Mirror, the source of darkness from which Shadow Link was originally summoned. He also learns that Shadow Link does not desire to follow Ganon, and in fact wishes to rule over Hyrule alongside Vio. Shadow Link simply hates humans and the world for spurning him as "just a shadow". However, after Vio is foiled in an attempt to shatter the mirror, Shadow Link discovers his betrayal and attempts to execute him in by dropping him into the lava of Death Mountain. Saved at the last minute by the three other Links, they confront Shadow Link, and with their new-found strength, destroy him with a combined Sword Beam attack.

Shadow Link is not killed, however, and is pulled by Ganon from the mirror again, dripping and shivering as he tries to resist entering the light. Seeing him in this state, Princess Zelda takes pity upon him. He attempts to spurn her but is momentarily moved by her words as she states that he should not fear the light, as he too is a hero. Driven by a desire to save her from the Dark Cloud, he disguises himself as Vio and aids the three other Links in their battle against Vaati. Realizing that the demon cannot be killed by the Four Sword alone however, he returns to the Dark Mirror, and in an act of self sacrifice he shatters it, destroying both Vaati and himself in the process. Before he vanishes, the four Links thank him, and tell him he will always be a part of them. Shadow Link makes a final appearance on the penultimate page of the manga, appearing as Link's shadow and giving a thumb's up.

Trivia

 * Dark Link and Shadow Link were once considered the same entity. However, since ALBW, it has been confirmed Shadow Link is a separate entity. He shares this feature with Metal Mario, Dark Mario, Shadow Sora/Roxas, Anti-Saix, Anti-Riku, Ventus and Vanitas.
 * Shadow Link, although being referred to as "shadow", is actually a demon.
 * Shadow Link, alongside Dark Link, has been subject to multiple creepypastas.