First of all to access this superbeig you need to have lv6+ and have completed Underwater quest line
no matter if you do alone or group - you need the effects that get rid of his dead rum.
if he accumulates that he becomes very very very hard to kill
To kill him alone, you need upgraded lagmur (1000+ flaudin rep and lv

and a bunch of sharker wraiths (can be bought from flaudin shop with 500+ rep)
in group same idea, just easier and can probably limit / eliminate use of sharker wraiths. if all group has lagmurs great, but not needed