Here is the full list of all 49 After Wave: Downfall achievements.
Complete Hard mode by Vulcan
Complete Normal mode by Phoenix
Complete Normal mode by Vulcan
Complete Easy mode by Snow
Complete Easy mode by Thunder
Complete Easy mode by Striker
Complete Easy mode by Vulcan
Complete Easy mode by Force
Complete Hard mode
Complete hard mode without resurrecting
Defeat the Deathrix and save the world.
Complete Hard mode by Force
Defeat the Lighting Dragon
Defeat the Long Legs
Complete Normal mode
Complete Normal mode by Force
Complete normal mode without resurrecting
Defeat the Hearth Whale Zombie
Defeat the Whale Zombie
Defeat the Turtle War
Score at least 5000000 points
Complete Easy mode
Complete Easy mode by Phoenix
Complete easy mode without resurrecting
Defeat the Giant Root
Defeat the Greedy Bear
Defeat the Frowzy Beaver
Defeat any boss without taking resurrecting
Score at least 1000000 points
Defeat the Giant Catfish
Get 50 combos
Get 100 combos
Score at least 100000 points
Score at least 500000 points
Complete the tutorial
Complete Arcade mode
Complete Hard mode by Phoenix
Complete Normal mode by Striker
Complete Hard mode by Striker
Complete Normal mode by Snow
Complete Hard mode by Snow
Complete Normal mode by Thunder
Complete Hard mode by Thunder
Upgrade to maximize all of your status
Kill 200 enemies
Kill 1000 enemies
Kill 5000 enemies
Get 300 combos
Score at least 10000000 points