Everything started well when Marceline and Bubblegum were making a type of serum in the lab. However, it was discovered that Marceline mixed up the reagents and caused an explosion of gas. While the gas was not extremely harmful, it started to affect the bodies of the girls on a genetic level. Bubblegum’s and Marceline began to develop breasts. They expanded to enormous dimensions. In the underside of the skirts, you could feel some strange sensations that something was very big. To discover the next chapter, begin watching comics.