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Alternatively, he'd rather forego said development because he doesn't want to be a killer.
Discussed: "Oh, look, the Big Bad is coming - guess Bob is going to show him he's not what he used to be."
Conversed: "That Bob is a hell of a lot tougher than he was last episode..."
In an effort to become more badass, Bob goes through Training from Hell to make himself stronger. The torment he undergoes destroys his psyche, which is only revealed later, at a pivotal point in the story.
Bob's attempt to take a level in badass transforms him From Nobody to Nightmare, as he discards his morality and empathy in favor of incredible power.