Images:

gw2-arcanus-obscurus-focus-1gw2-arcanus-obscurus-focus-2gw2-arcanus-obscurus-focus-3

Set:

Slot Item Name Trading Post Preview Code
Focus http://db.dulfy.net/item/27024 GW2 TP [&AgGQaQAA]

Where to Obtain:

Random drop from mystic forge (by combining 4 Level 75+ rare/exotic focuses) or from dungeon/fractal chests