Here is the full list of all 14 Balloon Blast achievements.
Get someone to run over your debris pile within 1 second of deploying it
Pop an opposing teams balloon by firing from at least 5 meters
Play for 60 seconds without a balloon
Take the acceleration cannon 15 times
Drop into a map 10 times
Join a server
Pop 3 balloons while you don't have one
Pop an opposing teams balloon
Pop a balloon while speed boosting
Pickup 15 pieces of debris
Enter the practice range
Take the acceleration cannon
Win a round of at least 100 points without losing your balloon
Make a server