The Gatling Gun Enemigo is a blue Enemigo with a tombola hat. He has his Gatling Gun mounted on a tripod pedestal in front of him, which he crouches behind, from which he shoots lots of little grey balls. He's a stationary Enemigo and only aims in one direction. It can be killed with the damage of 25 fists when Cactus McCoy has a punching level of 1.
In Cactus McCoy and The Curse of Thorns, a good strategy for defeating the Gatling Enemigos would be to get behind them, as they cannot turn back and are completely vulnerable when hit from there.
Trivia
Technically, the bullets don't come out of the barrel of the gun, but rather the side, which is an artwork mistake. This can be seen in the picture to the right.