Cartoon Creature: Word of God says, "[T.U.F.F.] always knows [Keswick] will have the answer, but they just don't know what kind of animal he is." Its revealed in a later episode that Keswick is actually part of his own species, also called Keswick. They have quite an unusual life cycle, including a 'platypus phase' where they shoot toxic quills when they hiccup.
Retired Badass: The Chief was once T.U.F.F.'s top agent and an amazing fighter. In one episode, he comes out of retirement to help Dudley deal with the Chameleon. While things don't work out well at first, Dudley manages to give him a pep talk and he shows he's still got it by beating up the Chameleon.
Even Evil Has Standards: Snaptrap would never kill anybody on their birthday without letting them celebrate it first. "No one's THAT evil!"
When Snaptrap asks for suggestions on how to get revenge on the "Meanies" at the monotrail for not letting them ride, Fransisco suggests that they eat them. Snaptrap flat-out states it's just "Dark and Disturbing".
The reason why Snaptrap tells the Agents his latest plan is because he considers it's rude not to.
Too Dumb to Live: Snaptrap is a mild example, particularly in "Mission: Really Big Mission" where his get rich quick scheme for the episode will also destroy the entire planet. Even The Chameleon calls him out on his embarrassing case of Didn't Think This Through.
Vocal Evolution: His voice was initially a bit deeper, but cracked constantly - but by the end of the first season his voice became more consistently high-pitched, lessening the Ed Wynn aspect of his voice.