Here is the full list of all 12 1 vs 100 achievements worth 200 gamerscore. It takes around 8-10 hours to unlock all of the achievements on Xbox 360.
In a single 1 vs 100 Live round, maxed out your Avatar Action 10 times.
Answered a total of 500 questions.
Your team of four achieved a simultaneous Streak of three consecutive correct answers.
Answered a total of 100 questions correctly.
In a single round, achieved a Streak of 12 consecutive correct answers.
In a single round, received six consecutive Instant Answer Bonuses.
Answered instantly and incorrectly three times in a row.
Got three consecutive questions right while receiving an Instant Answer Bonus for each.
Answered a total of 25 questions correctly.
Extended Play: In a single round, saved up the maximum of three Skips.
In a single round, scored a total of 1300 points through time bonuses.
In a single round, achieved a Streak of five consecutive correct answers.