The Genlock Shapeshifter can be found in Fort Drakon, first floor, during the final battle, shortly after the Genlock Conjurer encounter. It can shapeshift into Blighted Animals. Its transformations are very similar to those of the Shapeshifter specialization, with some differences. It is rare for it to become a Flying Swarm and it can become a Blight Wolf, which is not one of the Shapeshifter's spells.
See: Dragon Age: Origins