Here is the full list of all 80 Rhythm Zone achievements.
Accept and win your first Challenge
Send your first Challenge
100% a Friends Challenge that was sent to you
At least double your friends’ Score on a Challenge they Sent
Accept and Complete 10 Challenges
Accept and Complete 25 Challenges
Accept and Complete 50 Challenges
Accept and Complete 100 Challenges
Accept and Complete 500 Challenges
Win an accepted Challenge with any song set on Easy Difficulty
Win an accepted Challenge with any song set on medium Difficulty
Win an accepted Challenge on any song set on Hard Difficulty
Win an accepted Challenge on any song set on Expert Difficulty