Becoming the Mask: In early episodes, he resented having to wear the rat costume. As Flanderization kicked in, he apparently began to actually identify himself as a man in a rat suit as if it were his species(as well as the fact that friends and family members inexplicably became people in rat suits as well).
Genre Savvy: Lester would occasionally succumb to the inevitable and inform Beakman that he was not going to pooh-pooh the latest Challenge, because he knew from experience Beakman was going to turn out to be right and make Lester look foolish in the process.
The Lab Rat: Subverted, despite being the guy in the lab in the rat suit.
Audience Surrogate / The Watson: Beakman's assistants help think through the answer, ask the obvious questions, and generally keep Beakman moving toward a response to the readers' questions.
Genki Girl: All three were highly energetic, particularly when rushing in from off-screen or during the intro to Beakmania.
Josie (Alanna Ubach)
Awesome Moment of Crowning: The last segment of Josie's last episode shows kids how they can do their own research (using the question "How do fireworks make those neat colors?" as an example). Beakman points her to resources, but Josie does most of the legwork and provides the final answer herself.