aqua goblin tidal lord  

As well as bashing hard, Tidal lords have some sort of magic that kills instantly. I was fully healed with 300 hp and died immediately with the message "you are surrounded by pain". The other MOB that did that to me were Brownies.

All aqua goblins in this zone are archers and carry a bow and 4 arrows at loot. They will pause and shoot arrows at you as they move toward you. All aqua goblins are proficient swimmers and will flee to the lake usually if they are low on hp. Root or snare unless you are proficient at underwater combat. Note that some parts of the lake bottom are quite deep and you may not make it back to the surface if you swim all the way to the bottom.

Tidal lords can hit up to 50 and also bash. In addition to the quest items noted by other posters, they also carry words, bronze weapons and a platinum or 3 in cash. In addition to the bow and arrows all aquas carry. Note that the water rings seem quite common loot about 1 in 5 or so. The shells are rarer, maybe 1 in 10. Both items can be part of the same looted goblin. The ring and shell are LORE.

There is also a named Aqua Lord named Bilge. He carries the Reed Belt (+WIS)
among I think other items. He seems to be a rare spawn and no one seems to know where he would spawn.