Here is the full list of all 20 Ultimate Arena achievements.
Have 1000 Fighters in your Library
Kill 90 Fighters with Landmines in a Single Game
Kill 50 Fighters with Landmines in a Single Game
Have a Single Game last 10 Days
Have a Single Game last a Week.
Reach 80 Homicides in a Single Game
Have 500 Fighters in your Library
Reach 60 Homicides in a Single Game
Have a Fighter get off Mr. Troy's Wild Ride
Reach 1000 Updates in a Single Game
Read the Credits
Click the Twitter button on the Main Menu
Click the Facebook button on the Main Menu
Have 30 Events in your Library
Have a Fighter Reach -50% Sanity
Have 200 Fighters in your Library
Reach 500 Updates in a Single Game
Have 100 Fighters in your Library
Have 10 Events in your Library
Visit the Github page for Ultimate Arena