Ruined Dragon

The Ruined Dragon, also known as the Lord of Lightning, is a giant dark purple dragon encountered in the Ruined Kingdom in Super Mario Odyssey. According to Crumbleden's brochure, it is thought that the tower there was meant for him to land on it, while an altar with the shape of his head was made near said tower to talk to him. It is also implied that he's the responsible for reducing Crumbleden to ruins.

Super Mario Odyssey
While traveling to Bowser's Kingdom on the Odyssey, Bowser is shown standing on the dragon's head, ordering him to attack through a powerful magenta lightning bolt that damages the Odyssey heavily and forces it to land on Crumbleden.

There, he's met on the ruins of the tower and attacks Mario through two types of attacks: the first one are magenta lightning bolts from his mouth that hits the ground in front of him, geneating various rotating spiked wheels made of electricity that are able to slightly change direction to chase Mario. The more the ruined Dragon is hit, the more spiked wheels are generated through this method. The second consists in electrifying his head and slamming the ground with it, generating various magenta electrical sparks that diffuse in all direction and have to be avoided. A few seconds after the second attack, the head stops being electrified and the dragon is forced to rest, allowing Mario to jump on his head and use Cappy to remove various sword-shaped pins on his head that keep a crown shaped after Bowser's head into place. Sometimes removing a pin might make a dark violet Burrbo come out. Once all pins are removed, the crown disappears and Mario is able to ground pound his head to hit him. Every time he's hit, the number of pins keeping the crown in place increases. Once he's hit for the third time, he faints, and leaves a Multi Moon that is needed for the Odyssey to be repaired.

Unlike other bosses, he doesn't explode after being defeated and instead rests hanging on the tower of Crumbleden. Mario can even talk to him by reaching the plaza on the top of said tower. After activating the Moon Rock, a Power Moon can also be obtained by throwing Cappy at the tip of his upper right horn.

Physical appearance
The Ruined Dragon is a huge dark purple dragon. He's rather thin and features two rather long legs culminating in what appears to be three-toed feet, as well as two long arms culminating in hands having three fingers and a thumb, with white sharp claws. His wings are huge with respect to the rest of the body and features five fingers, with two additional claws on the top, one at the carpometacarpal joint, the other presumably at the metacarpophalangeal joint of the longest finger. The are dark purple at the top, gradually becoming red at the bottom. The body is fully covered by big scales, while its lower part until the head is covered by bigger plates and has a lighter pink color. The Ruined Dragon has a long neck and an head with a long muzzle. His mouth has gums fully covered by teeth and features a long and thin tongue, curved at the tip. His eyes are round and feature a black sclera, irises which are yellow with a red border and black vertical slit pupils. He features on the back of each side of the head two horns pointing backward which are segmented and doubly curved, with the upper horn being bigger than the lower one, and in general the whole head is covered by smaller horns, two of them have the shape of teeth and are found almost at the end of the muzzle. The head also features a peculiar segmentation forming vertical bands which are more visible on the lower part of the muzzle. The upper tip of the muzzle is slightly protruding and features two relatively small nostrils. When first meeting him, the Ruined Dragon is seen wearing a golden crown featuring the shape of Bowser's head on it, as well as various horns and a black cloth with golden motifs similar to the ones seen in Bowser's Kingdom, which is kept into place by chains that are fixed to the dragon's head through some golden sword-shaped pins, identical to the sword-shaped stakes found in Crumbleden. After being defeated, the Ruined Dragon no longer wears said crown.

Compared to other dragons (and most creatures in general) in the Mario franchise, the Ruined Dragon has a more "realistic" design, with detailed textures and little cartoonish exaggeration, just like the Ruined Kingdom he's found in.

Quotes

 * "So...tired..." - Super Mario Odyssey