Unlike so many other monsters inspired by classic mythology, the kraken is a legendary sea monster of giant size that is said to dwell off the coasts of Norway and Greenland. It’s very likely that such a legend originated from sightings of giant squids, but as it was described for the first time in 1752, the kraken is a very modern legend in comparison to other monsters in D&D. Its first apparition for the game was in the 1e Monster Manual II, in 1983.
Krakens resemble gigantic squids, with large tentacles emerging from a streamlined body. A kraken usually has eight tentacles, two which are nearly 60-feet-long and covered with barbs, and six which are 30-feet-long. They have a beak-like mouth beneath their swarms of tentacles.
Unlike squids, though, krakens are highly intelligent, and usually extremely malicious. They take delight in dragging unknowing prey deep beneath the waves. They have been known to build giant communities of stolen humanoid slaves in air pockets deep beneath the ocean.
According to the ancient legends of the sahuagin, the krakens have been around for millennia. Their legends speak of a great war between the krakens and the dragons during the Age of Demons, though the krakens’ allegiance is nothing but clear. Krakens have survived over the centuries, becoming god-like beings in the eyes of the sahuagin. Some clans of sahuagin worship these malevolent creatures, while others see the krakens as an affront to their god Shargon and seek to destroy them.
House Lyrandar features a kraken’s tentacles in its crest, taken after the firstborn of their house, Lyran, who was said to have the blessing of Arawai and used krakens to smite his pirate foes. A small cult within House Lyrandar, the Storm Front, believe that krakens are actually the greatest heirs of House Lyrandar, and that they too can become krakens if they gain enough power. There might be some truth to this, since House Lyrandar ships have been free from attacks by the increased kraken activity in the Thunder Sea. These krakens are not to be confused with Calynden d’Lyrandar from Stormreach, often called “the Kraken”.
In your campaign
In 5e, krakens are legendary monsters, which gives them special abilities in their lairs. In a 6-mile radius from the center of their lair, krakens can alter the weather at will, water elementals coalesce and also aquatic creatures with an Intelligence score of 2 or lower are charmed by the kraken and aggressive toward intruders in the area.
When used them in an encounter, krakens use their giant tentacles to grab and crush ships and victims sailing the seas. They use their smaller tentacles to grab unknowing prey, dragging them deep beneath the sea. A kraken’s tentacle is extremely strong, and can crush a small ship. They move at great speeds, and can use their bodies to ram vessels. Much like a squid, a kraken can jet quickly in the opposite direction, firing off a cloud of ink as it goes. Krakens also have the ability to control the weather, and will use this to whip up storms to besiege their targets. In 4e, krakens can speak both Aquan and Common, and are telepathic. They can use this telepathy to take partial control of other sea life, using them as minions. They possess darkvision to see beneath the waves.
You can see the full 5e stats for the kraken here.