- "We were born of nightmares... To take over this world, we made the Wind Fish sleep endlessly! If the Wind Fish doesn't wake up, this island will never disappear! We would have been the masters of this place..."
- — Nightmare
Nightmare is the leader of the Nightmares and the final boss of The Legend of Zelda: Link's Awakening. It is the dark force behind the Wind Fish's perpetual slumber. Although Nightmare's true form is never confirmed, it is believed by many that DethI, its shadowy, one-eyed form, is its true shape, due to it being Nightmare's only original form. Nightmare can create other Nightmares, all of which act as individual entities. Each of them seem to share similar personalities, however, with their main goal being to stop Link from awakening the Wind Fish. One of its incarnation went as far as to try and trick Link, lying to him that he would also disappear if the Wind Fish awoke.
The exact nature or creation of Nightmare is vague, but its goal is clear: making the Wind Fish sleep endlessly, locked in a tormenting nightmare so that Koholint Island retains its existence so that Nightmare may rule it forever. Nightmare presumably has the power to take the shape of any foe encountered in Link's past, including his most fearsome adversary, Ganon.
Nightmare resides in the Wind Fish's Egg on Mt. Tamaranch. To reach Nightmare, Link must enter the Egg after collecting each of the eight Instruments of the Sirens from the dungeons of Koholint Island. If the hero has obtained the Magnifying Lens and read Dark Secrets And Mysteries Of Koholint, he will know which path to take to reach Nightmare's lair. Once he finds the beast's chamber, Link battles the creature and successfully slays it.
Once Nightmare is defeated, Link and the Wind Fish awaken and Koholint Island ceases to exist.
Nightmare appears on the Koholint Island DLC Map in Adventure Mode. Nightmare will shroud enemies on certain squares, preventing the player from fighting there until it is dispelled using the eight Instruments of the Sirens Item Cards. As long was the Wind Fish's Egg slumbers, Nightmare will continue to appear on the Koholint Adventure map.
- "We are born from nightmares... In order to maintain order in this world enclosed in a dream while the 'Wind Fish' was given eternal sleep... We were born to prevent the awakening, because the island will disappear... WE ARE GOD!!!"
- — Nightmare
Nightmare is for the most part the same, save for some different dialogue. It refers to itself as a god and claims that it is responsible for preventing the end of its world's existence. It is unknown whether or not there is any truth behind its claim of godhood.
Nightmare's name, obviously, is a reference to the eternal slumber it is keeping the Wind Fish in. Nightmare's alternative name, DethI (pronounced "Death I"), may be a play on the word "death eye".