Robot Arm (official name unknown) is a minor stage enemy exclusive of the NES version Strider.
Appears in China.
The Robot Arm is a strange contraption found only in Enterprise's Chinese base, in the entrance to the eastern tower. A red and blue machine with a spinning top resembling a mechanical claw, the Robot Arm is a stationary enemy which can only attack by spinning its claw around, hitting Hiryu through direct contact.
The Robot Arm can only be damaged on its top area, so one has to strike it while standing very close to the machine.