Kraken[]
Kraken is an optional boss found in the Sea Cave in Chapter 25. It has many tentacles that can attack your party members or grab you and throw you around. If Zael is grabbed whilst having Gathering active, Gathering will be canceled. When its head is above surface, it generates magic circles that summon spikes from the ground inflicting Doom on impact. It can also damage the ceiling by shooting a powerful beam, causing the ceiling to collapse onto your party members.
To defeat it, you have to cut off all of its tentacles. To do this, you can activate Gathering, and store energy to Gathering Burst, or you can just cut them off one by one. When you are done, prepare to run up a wall and Vertical Slice the Kraken. The first time you fight it, make sure Lowell is not casting his ice magic, as Kraken can absorb Lowell's magic. You can also command Dagran and Syrenne to Full Guard as well. Your other mages should retreat, while you do most of the damage. So, the best way to kill it is: Gather, Endure, Burst, Vertical Slice. Rinse and repeat.
Berserk Kraken[]
Berserk Kraken is a stronger form of the original Kraken and also another optional boss found in Chapter 43, as well as the true final boss. It's strikingly similar to Kraken except it doesn't inflict Doom. Instead the tentacles and its attack itself causes Sticky, making Zael and the others hard to move. Other differences between the two is that Berserk Kraken is pink in color. In this Chapter, it is responsible for contaminating the water in the cave and causing the Reptids underground to go "mad."
It drops an Ancient Alloy when defeated. Character dialouge implies that it's the original Kraken that also became "mad". Also, despite the mission being optional, the fact that Beserk Kraken is the boss of Chapter 43 makes it the true final boss of the game.
Kraken Online[]
You can also fight Kraken online in Co-Op. The same strategy applies; however, you can't use vertical slice, as it is too overpowered with other players. It has the same attacks as during the single-player, but it has more health and defense. It also summons Sea Reptids to come out and play and inflict Sticky. Its tentacles can also appear to have the "Nitro" effect on them, which makes them slightly faster and stronger than they originally were.