Remain Puffed is a medal in Plants vs. Zombies: Battle for Neighborville. It is awarded by collecting 100 marshmallows.
The name is a reference to Stay Puft Marshmallow Man, a fictional character from the Ghostbusters franchise, which sometimes appears as a giant, lumbering paranormal monster.
Dr. Zomboss didn't want to abandon the Z-Tech Factory, crown jewel of his empire. He just didn't want to get publicly spanked by an entire forest. Understandable!