Here is the full list of all 12 Joust achievements worth 200 gamerscore. It takes around 80-100 hours to unlock all of the achievements on Xbox 360.
Make your way to wave 30 using default settings
Stay in wave 1 for 120 seconds without dying while using default settings
Finish wave 20 on Xbox Live with another player using default settings
Get 1st place on in game score board using default settings
Defeat 3 Pterodactyls in one game using default settings
Make your way to wave 10 using default settings
Play on Xbox Live Ranked VERSUS and gain the rank of 5
Finish wave 5 on Xbox Live with another player using default settings
Make your way to wave 5 using default settings
Find a way to defeat a Pterodactyl
Finish wave 1 without dying while using default settings
Make your way to wave 100 using default settings