Metal Plugger is an enemy from Invasion: Going Personal that is let out from the helicopter by The Gruppy Leader which takes place at the end of world 3. Although it is its only appearance in the game, it is very powerful and aggressive. It uses more tactical moves than the main villain to get a player hit by planting mines on the way and shooting out homing missiles at the same time while he bounces toward the player. In addition to all of this, its mechanical body causes a very big seismic pound when landing.
It has less health than The Gruppy Leader and can be hit by jumping on it's head, but seems like it's the most difficult enemy because of it's moves. At the same time, there is a greater chance that this enemy can be killed quickly and easily by luck when attacking above while The Gruppy Leader never can be beaten by luck.