Like Father, Like Son
Like Father, Like Son is the final level of the story mode in the Bowser Jr.'s Journey mode of Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey, and involves the final battle with the Best Fitness Friends.
After Bowser Jr. and the Koopalings reach the Best Fitness Friends, Dieter questions Bowser Jr. on whether or not Bowser and his minions are evil, a point made from constantly kidnapping Princess Peach and inconveniencing a plumber, which Bowser Jr. denies, stating "good and evil are outdated".
The final battle then commences, with the first round consisting of fighting all three; Beef is a regular troop backed up by several Fawfulcopters and Borps, Dieter is the first officer and uses Doppelganger, and Kaley is the captain. After they are defeated the first time, they all take Malatone Formula:X, and Dieter threatens doom for Fawful, the Mushroom Kingdom and Bowser Jr.'s army. The second round has Beef as the captain, who uses Showdown. The third round has Dieter and Kaley reprise their roles from the first round, except Kaley can use Lightning. The fourth round once again has Beef as a regular troop, with Kaley and Dieter swapping roles. This time, Kaley uses Super Counter and Dieter uses Call for Backup to summon two Malatone-infected Borps. After their defeat on round four, they merge together into one giant horrifying monster, using dark doppelgangers of the Koopalings as its troops. Bowser Jr.'s and the First Officer's CP is fully restored at the start of this round. This monster begins by using Rally and then Fitness Vortex to inhale Bowser Jr.'s Snack Time and Showdown/Volleybomb/Shy Guy Swarm captain commands, rendering them unusable for the battle. It then uses Cyclone Breath to temporarily blow some allies away from the battlefield. Among its other captain commands involves two uses of Mystery Box, the first time damaging all allies and the second time restoring 30% HP of all enemies, and finally it uses Malatone Charge to take another piece of Malatone Formula:X and increase all its stats.
After the BFFs' ultimate defeat, Bowser Jr. and the Koopalings go out to the balcony and spot the Dark Star exploding. Bowser Jr. had a strong feeling that Bowser was the one who destroyed it, and wanted to wait for him to return before celebrating. However, Roy begun the celebrations immediately, prompting Bowser Jr. to join him. When Bowser does return, he rests up due to injuries from fighting the Mario Bros. while the minions repair the castle.
This level is unique for having two themes. The normal boss theme plays for rounds one to four, then for round five a new theme exclusive to this battle plays.
First Officer quotes
After the final boss produces dark clones of the Koopalings, the player's First Officer says something before Bowser Jr. tells the Best Fitness Friends that he has had enough of their attempt to take over Bowser's Castle and that he'll have to answer to him.