Choomba

Choombas are a kind of giant, metallic, locomotive-type Goomba found in the game Mario & Luigi: Bowser's Inside Story. They have coal-black bodies, red eyes, yellow-glowing pupils and a chimney on the top of their heads. They are associated with Coalbits, which will jump into a Choomba's head during battle to make it attack more. A Choomba will charge up its attack by walking back and shooting smoke out of it's head showing either a shell or a fist; the smoke will appear in a different pattern each time. The Choomba will then charge into Bowser, who needs to withdraw into his shell when Choomba jumps on him and needs to punch the Choomba when it runs into him depending on what command is shown in the smoke. Choombas also appear in the battle with the Fawful Express. Groups of four of them come out of the Fawful Express to attack Bowser. To counter this attack, the player must tap the area the Choombas are coming at him in and stomp them.

Trivia
Coding for Choombas were found in the games programming that revealed Choombas were originally able to be fought by the Mario Bros., and they had smoke signs that smoked an M for Mario or a L for Luigi.