A villain or evil character; a bad person, especially in stories, games, or movies; British slang for someone who behaves badly or criminally.
Alternative spelling of 'baddie' using '-y' diminutive suffix instead of '-ie'; both forms are equally valid informal noun creations from 'bad,' common in British English by the 20th century.
The choice between 'baddy' and 'baddie' is purely stylistic (like 'kitty' vs. 'kittie'), but it shows how English speakers instinctively add diminutive suffixes to make serious concepts more playful—we don't say 'bad person,' we say 'baddy,' turning morality into child's play language.
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