Best Fitness Friends

The Best Fitness Friends (also known as the Brute Force Federation, BFF for short) are a group of enemies in Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey. Posing as pharmaceutical reps with a cure for the Blorbs, they help Fawful infiltrate Bowser's Castle and aim to take out the Koopalings to stop them interfering with Fawful's plans.

Members of this group include Dieter, a thin tie-wearing being who acts as its leader, Kaley, a blue drug-addled female being who attacks with sound and flies like a bird, and Beef, a muscular pink individual who provides the group's muscle.

History
During the events of Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey, the Best Fitness Friends infiltrate Bowser's Castle on Fawful's orders. When inside, they offer to sell the Koopalings Skeletone Formula:D, saying it is a cure for the Blorbs (which they then demonstrate on one of the nearby Goombas).

However, they then reveal they do not have any more of the formula, and that the Koopalings will need to buy the recipe and make it themselves if they want any more.

This turns out to be a ploy to leave Bowser's Castle defenseless, as well as provide the Friends with a chance to get rid of the Koopalings and Bowser Jr. They do this by secretly following Bowser Jr. and the Koopalings around the kingdom, attempting to kill them and steal the ingredients in the process. In this time, they seemingly dispatch Ludwig, chuck Iggy Koopa off a cliff, and reveal their true identity as the Brute Force Federation, in addition to revealing that the Skeletone Formula:X has a secret power that they plan to utilize.

This power turns out to be mind control, which is made possible by mixing the formula with Malodorius Fibbian to create Malatone Formula:X. Said power is then used to brainwash Morton and turn him against Bowser Jr., with the BFF stating that they'll eventually infect all of Fawful's army the same way in future, with their eventual plan being to overthrow Fawful and take control for themselves.

From there on, the BFF encounter Bowser Jr. and the Koopalings a few more times. In one of these, they actually succeed in defeating them, albeit before getting thwarted by Captain Goomba, Boo, Shy Guy, and Koopa Troopa from the previous title. They also try and stop the group by sending out waves of brainwashed minions.

Eventually, Bowser Jr. and co track down the group in Bowser's Castle, where they face them in a final battle. After defeating them both individually and as a group, the Best Fitness Friends merge into a giant Malatone:X fueled monstrosity with incredible powers.

Bowser Jr. and his troops defeat them for good and get back the Skeletone and Castle in the process.

Technology

 * Skeletone Formula:X
 * Malatone Formula:X