From EZ Server Wiki
Arthicrex is an EZ Server Custom Zone, it is generally equivalent to Cazic Thule and drops the same armor molds and Essence of Cazic Thule that drop in Cazic Thule. Arthicrex contains many of the same lizardman type mobs as Cazic Thule, along with a variety of other mobs types.
Arthicrex zones into a cave area, where you will find a Noobie Merchant and Banker Once you clear your way out of the cave, there is much more open space than in Cazic Thule, and is much easier for auto-following bots to stick with you. Generally mobs are in packs, which like most of early EZ Server content, are easily pulled out solo.
Much of the loot in Arthicrex is identical to Cazic Thule, however several named bosses will spawn from random placeholders, and drop loot such as Juniper's Ring (ring with clickable buff) and Cazic's Health (a 400 HP type 24 Health Augment).