Tentacle Attack
Kraken damages 3 units in your team. Low damage and he does not pushback like in campaign, so really easy to deal with or just completely ignore.
Shielders / buffers are usually enough for this fight, healers are not needed unless you are low level or they are hybrid buffers like Ria.
Summon Underling
Every 20 seconds Kraken will summon an underling with the same level as him. This doesn’t change the fight much since the fish will die pretty fast anyway.
Weapons with Added Target will help deal with the summon while still damaging Kraken.
Hulking Frame
Kraken ignores 20% damage reduction, this effect cannot be removed. You can ignore this as long as you have a unit to sustain your team or provide shields (Erin, Ria, etc.).
Knockback Immunity
A passive you don’t have to worry about at all since we barely have any units in the game that can move bosses.