Yes, sir? Oops! Dr. sir!
~ Mary to Krassman

Mary is the (former) secondary antagonist of Kermit's Swamp Years. She is Dr. Krassman's assistant.

Krassman tries to get the frogs in the swamp for his biology class at George Washington High School. His antagonism to frogs was due to a childhood trauma, when he intended to prove a frog talked to him, but he was embarrassed.

One day, in his biology class, when he is about to dissect Croaker, he, the other frogs, Mary, and the high school students keep chanting, "Let the frogs go!". Suddenly, Krassman changes.