The Omega-onion?! is the last level in Cavi Cape in the Bowser Jr.'s Journey mode of Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey.
Morton finds a red Oho Jee with the Omega-onion, for whom he mistakes the Oho Jee for it. The Oho Jee exclaims that he was not the onion and that he was planning to eat it so he can get the energy he needs from it. Morton demands the Oho Jee to give the Omega-onion to him, but the Oho Jee refuses. They then get fed up in an argument that lasted half an hour. Bowser Jr. and Kamek run up to see what the commotion was about, and find the Omega-onion, in which Bowser Jr. also mistakes the Oho Jee for. Kamek tells Bowser Jr. that the onion was right next to him. The Oho Jee challenges the three to a battle and that if he loses he will give them the Omega-onion. Bowser Jr. did not understand what the Oho Jee was saying. Morton tells Bowser Jr. that the Oho Jee was about to battle him and encourages him. Bowser Jr. tells the two that they were both terrible talkers and that he'll have to fight him just to get the onion. After the battle, the Oho Jee gives up telling the three that the onion was all theirs and goes home. Kamek demands Bowser Jr. to get the onion, in which he does. Bowser Jr. thinks to himself that if he finds the last ingredient and makes the homemade Skeletone, he can turn all the blorbed Goombas back to normal and his dad would be very proud of him. He tells Kamek and Morton that he can handle just about anything by himself without anyone listening to him. Kamek asks Bowser Jr. on what the last ingredient was. Bowser Jr. remembered what it was, but he could not recall on what it was called at first and asks if it has to do with ice. Kamek suddenly remembers it was called "Ever Ice", which was found below the castle inside the Lava Lair. He then flashes back to a moment where Bowser Jr. told Bowser about the Ever Ice and that he wants to eat it. Kamek, from afar, was watching the conversation. Several days later, Bowser tells his son that he found the Ever Ice that he was so excited for. Bowser Jr. somehow forgot about the Ever Ice saying he did not need it anymore, which frustrates the Koopa king. Bowser Jr. tells Bowser that there was something more important he needed, which was a toy he wanted. Kamek, also frustrated about Bowser Jr. forgetting that he wanted some Ever Ice, thought to himself that he was the one to find the Ever Ice and that he might add something to it after 36 hours of searching. Kamek thought Bowser Jr. would want the ice again one day and stored all of it in a freezer in the castle basement. After thinking of that moment, Bowser Jr. tells Kamek to hurry on to Bowser's Castle so they could get the Ever Ice. Morton starts to worry about where the other Koopalings could be, along with Kamek. Kaley, Dieter and Beef (who was Ludwig in disguise) overhear this and hurry on to Bowser's Castle to steal it.