To get the Eridian weapon early on, have a Siren character. Return to Fyrestone in the Arid Badlands. After killing the Mothrakk, a Eridian weapon will drop. You must search everywhere to find it. Note: To kill the Mothrakk easily, when it is low on health, shoot warning shots to lure it towards you. Kill it while it tries to get close. The weapon should be Eridian Cannon (Berserker), Thunder Storm (Soldier) or Ball Blaster or Wave Blaster (Siren).