As you can see I encountered two invisable and invincable (i couldnt attack it) Gun Puppys in JK level.
Shows invisable Gun Puppy shooting
http://imageshack.us/photo/my-images/580/2012021800002c.jpg/
Shows Invisable Gun Puppy Stuned (from res'ing, not from vials cause i couldnt hit it)
http://imageshack.us/photo/my-images/828/2012021800003o.jpg/
After I killed all the normal enemies and opened the gate these two Invisable Gun Puppys went away.