When students are preparing to write a biased historical account, start by giving them 5 minutes to produce a personal list of "positive" adjectives (brave, clever, thoughtful, and so on).
Students then stand up, and in turn have to promptly suggest a word which is added to a class list. Any hesitation or repetition means they have to sit down.
The winner is the last person standing.
Repeat for "bad" words, then provide the complete list to the class to use in their written account.