So Basically, it goes like this: While Melvin Is at his lab, Small Poopypants breaks in and offers a Team-Up to him again, But This time Melvin is skeptical because the Last time he almost died. But Poopypants Manipulates him, and Melvin decided to accept the offer ( I Was going to make Melvin Change himself into a Cyborg, Adapting Melvinborg. What do you think? ). In The Final Climax, Captain Underpants gets smacked to the Hypno Ring Factory and goes to the Hypno Liquid maker. After the Climax, we see in the Post Credit Melvin is in the Hypno Factory. And picks one of Captain Underpants' nails ( That's Covered in The Hypno, too. ). And Vows revenge on George and Harold for Killing Poopypants. And puts the Nail on a DNA Maker thingy.