The fiend is an exalted eiroch utilized by the kett empire as shock trooper. The human Pathfinder of the Andromeda Initiative encountered these beasts while investigating the kett bases, notably during the rescue of Moshae Sjefa.
The fiend's body features greatly deviates from the standard eiroch's, in that spikes adorns the fiend's head and shoulders. Its armor also becomes significantly stronger, as does its physical strength. Fighting it alone is highly difficult without high-tier weaponry.
A fiend would be less threatening if you can take a high ground that it can't climb up to, then its attack would be limited to lobbing acid spit that can be easily dodged, alas that also mean its vulnerable exposed flesh - which primary locate at the back of its torso region - out of direct line of fire. Since rarely a fiend would attack alone - if not alongside other wildlife beasts then it's with a kett attack force - you might adopt this as a means to keep the fiend out of fight until you've dealt with other enemies in the field.
If fighting on the same level with a fiend is unavoidable, remember that it is far more agile then its bulk suggests, so constant moving will be a must to avoid it getting close. Use the jump jet to exploit flanking opportunity to shoot it at its exposed flesh. Since it's organic, fire-based tech power like incinerate will be very useful.