Luminous Krayfin

"The Luminous Krayfin thrives in a humid habitat and must feed on the Dragon Bloom, a most dangerous flower. Only then can it become a leviathan. Extremely dangerous. Pray you never see this monster on the seas."

- Bork Papers-School of Dragons

The Luminous Krayfin is a large Tidal class dragon that made its first appearance in the School of Dragons expansion "Secret of the Leviathan". As an adult, it becomes a Class 10 Leviathan, just like the Bewilderbeast.

Egg
The egg of the Krayfin was previously referred to as the "Mysterious Blue Orb". It is a large round egg that is a glowing cyan blue in color with darker blue swirls around its circumference.

The "Mysterious Blue Orb" was first seen in the School of Dragons Expansion "Battle for the Edge". In this expansion, the Dragon Hunters first had it, and later Harald Forkbeard steals it from the Hunters. At this time, the player is not sure what the Orb is.

The "Mysterious Blue Orb" reappears in the next School of Dragons expansion: "Return to Dragon Island". Through various quests, the player and the Dragon Riders gain control of the Orb, which the player realizes is an egg. The expansion ends with the egg hatching and Hiccup saying his famous line, "This changes everything". The following expansion, "Secret of the Leviathan", reveals that the egg has hatched into the Luminous Krayfin.

Hatchling and ShortWing
The Hatchling and Shortwing growth stages of the Krayfin are seen in School of Dragon's expansion, "Secret of the Leviathan". It has four short legs, each ending in a long flipper, and long wings. It is capable of long flight at this age. Its body is rotund and has a chunky short-snouted head. It has a line of luminescent spots trailing along its body. Depending on the lighting within the game, the Krayfin appears to be indigo or dark blue, gray at other times, and even dark green.

According to Hiccup, the Krayfin grows rapidly.

Adult and Leviathan Stage
These growth stages are unknown yet. However, the "Bork Papers" reveal that in order for the Krayfin to become a Leviathan (Tidal Class Titanwing), it needs to eat a plant called the Dragon Bloom.

Trivia

 * The Luminous Krayfin is the first Franchise dragon to start with the letter "L".
 * The Lycanwing also starts with an "L", but it is unknown if it truly exists.