Impossible, Mage - No unit loss.

[Metathron]

In my current game as impossible paladin, I attacked the kraken when I was about level 12, I think, with the following army composition:

Inquisitors
Archmages
Cannoneers
Giants
Royal Snakes

All in all, the fight wasn't tough at all. Used the snakes' lunge ability to attack the kraken directly, and used the giants as a tank to both attack the kraken and provoke it to attack the giants (so no devilfish summoning for some turns), which it did, and the giants could more than withstand its attack with its huge hit points, the archmage's shield, and an occasional heal spell.