Where can it be found

Waterbirth island dungeon, lowest level.

Tactic

The Dagannoth Supreme launches spines from his back that hit several people at a time. It's best to melee the Supreme, when he launches his spines, people who are further away are more likely to be hit than those standing near him. Also if you can get behind him that is great, as he only launches spines in front of him. As long as you have protect from ranged on, he isn't really that difficult.

Examine Message

The dagannoth king responsible for the death of the Bukalla.

Notes

Be careful in the lair, as the other two kings can hurt you if you are not using their specific protection prayer.