Skeldritch

Skeldritch is the sixth boss in. Its appearance is very similar to that of Stallord; it appears as a large skull with a spine that rises from the center of a large, ruinous room filled with sand, although it lacks arms and a ribcage, and it also sports a large, horned helmet. The skull is also more human-like than Stallord's beast-like skull.

Strategy
Skeldritch will fire large rocks at Link, at which point, he will need to use the Sand Wand to create walls of sand that will deflect the attacks. He can then push one of the rocks into a nearby catapult and fire it back to one of Skelditch's vertebrae to destroy it. However, the last three bones are protected by armor, and Link must get Skeldritch to face a different direction in order make his exposed point face a catapult and fire at the switch with an arrow while Skeldritch is in this position. Skeldritch will also shoot a laser from it's mouth to try and strike Link if and whenever possible. When merely the head is left, it will float around the arena, and try to ram into Link. If surrounded by a wall of sand, Skeldritch will attempt to break out, allowing Link to attack the ruby-like weak point on the back of his skull. Alternately, Link can lift himself up using the Sand Wand any time he is behind Skeldritch to reach the boss's weak point.

Trivia

 * In the PAL version of Spirit Tracks, Skeldritch is named Capbone. The name most likely derives from the words cap and bone, as the boss sports a helmet (cap) and is skeletal in appearance (bone).
 * Skeldritch's name is derived from the words "skeleton" and "eldritch". "Eldritch" is a word meaning "unearthly," "alien," "supernatural," "weird," "spooky," or "eerie."
 * The "hopping head" phase of the battle strongly resembles the last phase of the fight against Eox in Phantom Hourglass, complete with a vulnerable gem-like object on top of the boss's head.
 * Some believe that Skeldritch is what remains of Malladus's original body, since they both look similar-Skeldritch's skull is lit from the inside by a red light. Its mouth is rather snaggle-toothed, having three teeth on top and only two on the bottom. On its head is a helmet bearing two large horns. Beneath this helmet is a large red gem, which is the true weak point of the monster. Malladus's spirit is also rather skeletal in appearance, and through the eyes, nose-hole, and mouth shines a red light. The mouth bears three snaggly teeth on top, and only two on the bottom. When possessing Cole, Malladus has two big horns, and his weak spot is a large red gem on his head. Their attacks are similar as well-Skeldritch's two main attacks are a laser-like beam fired from the mouth, and large boulders launched out of those strange spinal orifices. Later in the battle the boulders turn red, as though heated. When Malladus is possessing Princess Zelda's body he fires a laser-like beam at Link and Phantom Zelda. Later, when possessing Cole, Malladus launches flaming boulders out of his mouth. Lastly their encounters are very similar-Skeldritch is imprisoned within the best guarded temple in the game. To enter the temple you first have to beat the three trials that protect it: a giant rock-monster, tunnels that bend the laws of physics, and a battalion of cannons. And then you have to get through the temple proper. Once in Skeldritch's chamber you will see that his body is stuck in the ground, leaving only its long spine and its skull to tower in the center. What's more, the Bow of Light, a weapon instrumental in the Spirits' defeat of Malladus the first time, is also in this temple. As though it was wanted close at hand should it be needed to subdue the monster in the temple. Malladus, too, has been imprisoned. Long before the start of the game his spirit was put deep within the earth. Then the Spirit Tracks were laid down to act as shackles, and they were powered by four very large Force Gems placed in four temples. And the Tower of Spirits was placed as a lock to hold it all together. (Unfortunately, that lock is also the place that allowed Malladus' spirit to be funnelled out into Zelda's body...)