Best Fitness Friends is the final boss of Bowser Jr's story in Mario & Luigi: Bowser Jr's Journey. It's a melatone-powered monstrosity created by the fusion of Deiter, Kaley, and Beef as a final resort in killing Bowser Jr. and his group. Their final confrontation was held in Bowser's castle, around the same time when Bowser, Mario, and Luigi were battling Dark Bowser, the Dark Star, and Dark Fawful at Princess Peach's castle.

Tier: 6-C

Classification: A fused Malatone Monstrosity

Powers and Abilities: Superhuman physical characteristics, teleportation, energy projection, air manipulation, statistics amplification, statistics reduction, summoning, duplication, fusionism, healing, power negation

Attack Potency: Island level (Fought Bowser Jr, Kamek, and all the Koopalings all at once)

Speed: Massively FTL+(Was able to keep up and react to Bowser Jr, and Kamek)

Lifting Strength: Unknown

Striking Strength: Island level

Durability: Island level (Tanked several hits from Bowser Jr, Kamek, and the Koopalings all at once)

Stamina: High

Range: Standard Melee Range. Tens of Meters with energy and wind-based attacks.

Standard Equipment: None

Intelligence: Average

Weakness: None notable

Notable Attacks and Techniques:

•Malatone Charge: BBF will drastically boost all of its stats.

•Summoning: BFF will create exact replicas of its foes and characters it met, sporting the exact same powers and abilities as the originals.

•Piercing Projectile: Fires a massive pink laser from its mouth.

•Fitness Vortex: BFF will suck the powers and abilities right out of the target, temporarily making them incapable in using it.

•Cyclone Breath: BFF exhales a gust of wind at his foes.

•Mystery Box: Summons a box that will either heal it and its allies, inflict damage on its opponents, or boost one of its stats.