From the Super Mario Wiki
The Malatone Formula:X is an item in Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey. It is a chemical created by the Best Fitness Friends, combining its base formula, Skeletone Formula:D and a Malodorous Fibbian's breath, in which it alters 97% of the victim's DNA as said by Dieter after the first round of the level, "Like Father, Like Son". It is first given to Morton, which turns him hostile toward Bowser Jr. and his minions. The formula is then used on more minions to turn them hostile as well. Enemies under effect of the formula have a purple fiery aura around them, have their stats increased, and are immune to the Deny command in combat, but their special skills can still be stopped by Ludwig's Stop and Drop command. The formula may appear in effect on an enemy at the start of a battle, or be given the formula by a captain in the middle of the battle, at which point all their stats will rise and some of their HP will be recovered. Broque Madame and King Bob-omb (the latter only in A Mighty Melee) behave like Malatone-infected enemies, despite not being infected themselves.