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 altar with the shape of his head in said location was built to talk to him or possibly confront him, with it being made to restrain the lightning. It is also implied that he's the responsible for reducing Crumbleden to ruins. His Japanese name, Crumbleden Dragon, indicates that the Ruined term in his name refers to the place he lives in rather than his physical condition.

History
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, generating 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 streams that diffuse in all direction and have to be avoided. Like in the case of the spiked wheels, the more the dragon is hit, the denser the streams are and thus the greater is their coverage of the surrounding area. 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. Each time a pin is removed a creature similar to a dark violet Burrbo comes out from where the pin was stuck and tries to hit Mario with electricity. 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.

The rematch in Peach's Castle is mostly the same, but the streams of electricity the dragon creates after slamming the ground with his head now appear in a vertical zigzag pattern, meaning Mario must jump over some areas and run under others. Also, the battlefield is icy, giving Mario less traction.

Unlike other bosses, he doesn't explode after being defeated and instead rests hanging on the tower of Crumbleden. If Mario gets on the plaza on top of it, he follows Mario with his eyes and closes them if Mario throws Cappy at them, and can even be talked to. 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, rather thin dragon. His long appendages contain three-toed feet and claws that contain three fingers and a thumb. His wings are huge with respect to the rest of the body and features five fingers. The are dark purple at the top, gradually becoming red at the bottom. The Ruined Dragon has a long neck and an head with a long muzzle. The features on the back of each side of the head has two horns pointing backward, with the upper horn being bigger than the lower one, and in general the whole head is covered by smaller horns.

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. His lower body is rarely seen.

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