Demon Train

The Demon Train is a massive, semi-sentient locomotive used by Chancellor Cole and Malladus, and a boss in Spirit Tracks. It comes from the Dark Realm, which Cole locates with the help of the Compass of Light made by Byrne. The train is first seen when Cole and Byrne appear in order to obtain Zelda's body for Malladus. After Cole successfully resurrects the Demon King by using Princess Zelda's body as a vessel, both Cole and Malladus escape to the Dark Realm using the Demon Train. Link and Zelda chase after them after they retrieve the Compass of Light from beneath the altar of the Tower of Spirits.

Once Link and Zelda make it inside the Dark Realm, they locate the Demon Train after defeating all of the Armored Trains roaming the realm's tracks, leading them to a battle against the Demon Train in order to be able to climb on top and face off Cole and Malladus.

Strategy
During the first segment of the battle, Link rides parallel to the Demon Train, at which he will need to fire with the cannon at the bomb barrels that the train prepares to fire upon Link. The second cart will have laser-firing cannons, which must also be destroyed before they attack Link. These laser cannons take two hits to destroy. Finally, Link will have caught up to the train's face, and then can proceed to attack, which must be repeated several times. Hitting each of the blue jewels on the side of the Demon Train's engine will cause the train to stop abruptly, allowing for easier access to the train's face. Each stage has a "time limit", and if the tracks run out before the stage is defeated, Link will fall off the tracks and into an abyss.

During the next part of the battle, the train is not fought, however Link and Zelda fight Cole and Malladus atop the Demon Train now that Malladus has taken over Zelda's physical body.

Trivia

 * The face of the Demon Train resembles mildly the face of Ganondorf, which led to it being commonly referred to as the "Ganon Train" leading up to the release of Spirit Tracks.
 * Although the Demon Train could possibly be based on generic real life steam engines, it's probably based more on the Japanese Class C62 steam engines.
 * The Demon Train's battle theme is slightly reminicent of Ganon's in Ocarina of Time.
 * The Demon Train is possibly the largest boss Link has ever fought, along with Eox, Dark Dragon, Bongo Bongo, Molgera, Morpheel, Skeldritch, Stallord, and Cragma (the latter one appearing in Spirit Tracks as well). Though most of these bosses are taller, the Demon Train is one of the longest and widest in horizontal size.
 * The Demon Train is referred to as the Dream Train in Hyrule Historia, which is possibly a mistranslation.