The Unspeakable Deep - achievement for beating the first boss

https://www.youtube.com/watch?v=G8-_hvKIPl0

The leviathan is the first boss of the game, and the player only gets one chance to beat it.
The boss does not appear again in New Game +.
Loot obtained if you are fast enough to get it when it drops:
A black and shimmering pearl; A drowned tome; about 400 coins; 8000 salt.
The paladin is a good class for this fight because it deals a lot of damage and has lightvessels to throw at the boss.
The cleric is also a good pick with Blessed Page for a damage boost.
Others can beat the leviathan as well.


Remove some equipment until your equipment load is under 25, mandatory for longer rolls.
Let him prepare his attack (see the two forms below) then roll behind him and hit him once then wait for him to turn around.

• If he crouches, roll twice (or roll once during his jump, more dangerous).
  
• If he stands, roll once.

Do not get cornered, get back to the center of the ship to lure him there.
Do not panic.
Do not risk attacking him too many times.