Lurker

Lurker is an expensive unit. But it has enough worth. They can hide under the ground. If enemies don't have detectors, they can't see your Lurkers. Once Lurkers hide under the ground, it is very difficult to destory them. This is because Lurker's spines suffer damage through the ground in a straight line from the Lurker to its target. The only weakness of the Lurker is that it is virtually defenseless while above ground. So when you use this unit, you must be careful on the ground.