Here is the full list of all 48 Flat Kingdom achievements.
Earn the true ending.
Defeat the secret boss.
Beat 50 Bunny Balls.
Beat 500 enemies.
Get all of the secret scrolls.
Buy all the hearts from the store.
Get 100% coins in Flatsgard.
Finish all of the side quests.
Get 100% coins in Flatepetl.
Get 100% coins in Flatelysium.
Earn the normal ending.
Complete the game in Flat Newbie.
Complete the game in Flat Hero.
Defeat the last boss.
Activate the last Checkpoint Guard.
Get the final journal page.
Defeat Hex.
Open the path to the sky tower.
Get 100% coins in Flat Forest.
Get 100% coins in Flatlantis.
Beat 50 Squidclops.
Get all the special abilities.
Defeat Fenrir.
Defeat the Norns.
Get all the coins.
Defeat Flatepetl.
Defeat Quetzal.
Change your shape 1000 times.
Get your first special ability.
Defeat Kraken.
Defeat Hank.
Defeat an enemy with two or more shapes.
Buy your first heart from the store.
Defeat Arachne.
Defeat Plantosaurus.
Get 1 Game Over.
Activate the first Checkpoint Guard.
Finish your first side quest.
Use your three forms to fight.
Beat a square enemy.
Beat a triangle enemy.
Beat a circle enemy.
Get 100 Game Overs.
Complete the game in Flat Legend.
Earn all of the achievements.
Beat 50 Sparks.
Beat 50 Roundowls.
Beat 1000 enemies.