Glitch to kill him in NG+ on PC09 Jun 2016 18:30
There is a levitation glitch using a ladder that allows to get back to the ship area and kill him. Here is how it goes :
1 - In the options, remap the jump and roll actions on a same button (preferably one easy to access, you will have to spam it)
2 - Go to the entrance of the festering banquet
3 - If you haven't yet, kick the ladder just above the entrance
4 - Get onto the ladder, (preferably on the lower part)
5 - Hold up, and press your roll + jump button repeatedly
You should start ascending up and backward, and eventually reach the boat area (that is actually up in the sky). Then you can attempt to kill the unspeakable deep and leave usinc a bell of return or a calling horn.
Using this method, it's possible to kill him in NG+, and he actually drops more salt!