Kraken is not that bad of a boss. For his attacks, all he does is change pools to make it hard to hit him, so he will disappear and reappear in different areas, plus he whips you with his tentacles, but you will be lucky if these things even hit you. If his tentacle is red when it hits you, it'll throw you and it may cause Confusion. His only annoying attacks are that he fires an Ink Blast at you that can cause Darkness and that he can release Ankher on you, though weak, they are annoying. Attack Kraken with long-ranged weapons, as running up to the thing and trying to hit him with anything else before he runs off will be rather annoying. As for Magic, stick with Salamander and probably the Knucks if you do use it, as that is your best bet. Either way, just do not give up your assault and you will come through this a winner.
