Here are some tips about the boss:
1) Octopus boss is more or less immobile. He does not require tanking at all, since almost all of his attacks are AOE. He will not even move beyond the water, although he will still spam his AOE skills from the water. This means you can go balls to the wall with DPS and not have to worry about aggro on this fight.
2) He has three primary attacks: a weak tidal wave(~1k dmg), a strong melee cleave(2-4k damage, depending) and an ink attack(no damage, lowers focus 25%)
3) There is no noticeable way to dodge his attacks, as we tried many different positioning angles.
From our testing runs, we determined that for party play, grouping up for optimal AOE healing would be the most solid way to sustain through the fight for characters that are not tanky enough. Also, this fight is most definitely a gear check, similar to how the first boss in OS was pre-nerf(not enough HP? come back later).
At 35, a good Prophet with, as earlier said, investment in Dark Prayer and Crimson Chain, would be the key to victory. Snowfall may also be beneficial except it heals quite slow and the radius is quite small, so you would have to be grouped up tightly.
another tip should be added.....
As all the attacks are AOE and you cant dodge any of them. its a GREAT idea to have the party grouped at the boss each with the lvl 25 assassin skill blind. 6 second 25% dmg reduction cycled by each party member = 30 seconds of great dmg reduction + their redemptions and a healer aoe healing makes the boss a lot more doable.