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Ever Ice is an item featured in Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey. It is an ingredient required to create Skeletone Formula:D, and is the third and final ingredient to be obtained throughout the course of the story. It is known as a special type of ice found in the Mushroom Kingdom that supposedly never melts.
After finding both the Giga-carrot and Omega-onion, Kamek informs Bowser Jr. that the Ever Ice is located safely underneath Bowser's Castle in the Lava Lair. It is then revealed that earlier on, Bowser Jr. told his father about this type of ice and requested some, desiring to eat it. Kamek, who was listening nearby, retrieved the Ever Ice after 36 hours of searching and brought it back within a few days, though Bowser Jr. was no longer interested in it. However, knowing that Bowser Jr. might want it again another day, he decided to store it in the freezer beneath the castle.
Upon remembering this, Bowser Jr. heads to Bowser's Castle alongside Morton and Kamek to retrieve the Ever Ice. After battling and defeating two remaining Shroobs in the cryogenic chamber, Bowser Jr. resists the temptation to eat it, and they take a sample of the Ever Ice, allowing them to finally make the Skeletone Formula:D. However, as none of them know how to do this, Kamek suggests that they take the ingredients to his friend in Blubble Lake, Broque Madame, which they do.