Mobley is Named Enemy in Borderlands 2. He is located in The Dust region on the Planet Pandora. You encounter him during and after the side quest “The Good, The Bad, and the Mordecai” at the Church on Booth Hill where he confronts Gettle.
You can farm Mobley for the Veruc as he is the dedicated loot source for this item. Mobley’s legendary item has a 10% drop chance.