Monty Bros.

The Monty Bros. (generically referred to as Montys in the Prima Guide ) are a group of five Monty Moles seen in Mario & Luigi: Bowser's Inside Story and its Nintendo 3DS remake, Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey. They were tasked by Bowser to do Project K, in which the Monty Bros. construct a railroad beneath the Mushroom Kingdom, with the idea being that Bowser can use it as an escape tunnel after kidnapping Princess Peach to return over to Bowser's Castle.

History
The Monty Bros. are minions of Bowser who are first encountered in the Underground Tunnel beneath Cavi Cape. Here, they are using a large drilling machine to drill a tunnel through to reach Toad Town. They had already drilled from Bowser's Castle to Cavi Cape, almost reaching Toad Town. Bowser, who had just spotted them, said that he did not remember giving that order. Die to the bedrock on the other side, Bowser began to help the Monty Bros. finish their assignment. During this, Mario and Luigi, inside Bowser's body, would then go to the Leg Outpost and stimulate his leg muscles to push the giant drill before its battery ran out (or, in this case, ninety seconds of minigame time). After the minigame, the drill then crashes, and Bowser apologizes for getting too carried away.

Later, the Monty Bros. appear in the treasure vault of Bowser's Castle, where they had built railway tracks around their tunnel. Upon seeing Bowser's shocked face at the tracks, the Monty Bros. reveal that they had betrayed him to join Fawful and the Fawful Foundation, therefore doing Project K on Fawful's behalf, and that they outsourced the actual hole drilling to some other Monty Bros. in the process. In the Prima guide, it is stated that the Monty Bros. repurposed the railroad network for Fawful to travel around the Mushroom Kingdom with ease. The Monty Bros. joke that remark that the Fawful Express tickets are too expensive that even Bowser's Castle could not pay for them. This angers Bowser a bit, so the Monty Bros. jump into the Fawful Express, which they had built the tracks. Once Bowser walked onto the tracks, the Fawful Express proceeds to push Bowser all along the train track, slamming him into a massive boulder. Bowser then is re-awakened by Mario and Luigi, turning him giant, and a battle against the Fawful Express and the Monty Bros. commences.

For most of the battle, the Monty Bros. drive the train or make repairs in the Fawful Mountain. Near the end of the battle, they wear yellow masks and have jetpacks to attempt to throw Fawful Bob-ombs at Bowser. Bowser can counterattack them by punching one of the Monty Bros. so that they instead drop bombs on the Fawful Express, dealing more damage to it. Once the Fawful Express has been destroy, the flying bits of debris from it fall onto the Monty Bros., crushing them.

In the original Mario & Luigi: Bowser's Inside Story, it is unclear whether the Monty Bros. survived because they do not appear again. In Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey, it appears the Monty Bros. survived because they were seen escaping the train before it became destroyed and are not hit by debris. When Bowser picks up the Fawful Express, one of the Monty Bros. land on his nose before escaping.

Trivia

 * Before the battle with the Fawful Express, only four of the five Monty Bros. can be seen. Earlier on, when Bowser first encounters the Monty Bros., four of them are outside while one is manning the drilling machine.
 * In Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey, most of the sprites for the Monty Bros. while they are above ground is almost identical to the Monty Mole sprites in Mario & Luigi: Superstar Saga + Bowser's Minions, with the only difference being that they are not wearing a bowtie.