The Best Fitness Friends are a trio of minions that serve Fawful. They only appear in Bowser Jr.'s Journey of Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey. Their real group name is the Brute Force Federation; in the Japanese version, they are called SS Company (short for Super Suppiler Company or Shin Satsu Company. Shin Satsu means Instant Kill).
- Dieter: the Ranged-type member. He can speak German and is very vain.
- Beef: the Melee-type member. He was absent during the first half of the game, with Ludwig being his doppelganger.
- Kaley: the Flying-type member.
- The three members can fuse into a monster; in the Japanese version it is called KGS3C.
The trio are seen first after Bowser leaves his castle in the cutscene where Fawful reveals his plan to take over it. He then sends the BFF to introduce the Skeletone Formula:D as a cure for the blorbs within the Koopa Troop army. Bowser Jr. and subsequently all the Koopalings that are guarding the castle eventually went off to find the ingredients, leaving only the minions within the castle, thus succeeding in the take over. Later on, Fawful is implied to have gotten the Vacuum Shroom from Dieter, who insults Fawful's other henceman Midbus as a slow pig in a cutscene of Dimble Wood. While Bowser Jr.'s party was searching for the Wigglers' Giga Carrot, they shadowed them in order to steal the ingredients once all are gathered. Ludwig senses this and departs, later on becoming Beef's doppelganger. Kaley then leaks info of Fawful's invasion onto Bowser's Castle to the remaining Koopalings.