From the Super Mario Wiki
The Skeletone Formula:D is an item in Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey. It is a chemical formula created by the Best Fitness Friends that is meant to cure the blorbs, as this is successfully demonstrated on a bloated Goomba, curing him instantly. The Best Fitness Friends then tell the Koopalings that there are three ingredients needed to create more of the formula, as the formula that was just used was the last one. The ingredients are a piece of a Giga-carrot, an Omega-onion, and Ever Ice.
Bowser Jr. and the Koopalings set out to find the ingredients and eventually find them all, but need the help of Broque Madame to combine them properly. Once Bowser Jr. has the completed formula, Kaley of the Best Fitness Friends swoops in to steal it, revealing that it was all a ploy to trick Bowser Jr. and his minions into making it. The Best Fitness Friends then combine the Skeletone Formula:D with a Malodorous Fibbian, turning it into Malatone Formula:X, which causes minions to become brainwashed and hostile to their previous allies, which is first demonstrated on Morton. The Malatone Formula:X also creates immunity to the Deny command in battle, though Ludwig's Stop and Drop command can still stop special skills from enemies infused with the formula.
Bowser Jr. and the Koopalings eventually managed to retrieve the Skeletone Formula:D upon defeating the Best Fitness Friends and distributed it to the blorbed Goombas. Bowser Jr. also offered some to his father, Bowser, with the latter accepting largely because he still felt bloated as a result of the Vacuum Shroom he had ingested earlier. However, despite Bowser Jr.'s warnings, Bowser ingested the entire container, causing him to lose too much of his mass.
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