Here is the full list of all 48 Flat Kingdom achievements.
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 all the special abilities.
Defeat Fenrir.
Defeat the Norns.
Defeat Flatepetl.
Defeat Quetzal.
Change your shape 1000 times.
Buy your first heart from the store.
Get your first special ability.
Defeat an enemy with two or more shapes.
Defeat Kraken.
Defeat Hank.
Defeat Arachne.
Get 1 Game Over.
Defeat Plantosaurus.
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.
Defeat the secret boss.
Finish all of the side quests.
Buy all the hearts from the store.
Get 100% coins in Flat Forest.
Get 100% coins in Flatlantis.
Get 100% coins in Flatepetl.
Get 100% coins in Flatsgard.
Get 100% coins in Flatelysium.
Get all the coins.
Get all of the secret scrolls.
Get 100 Game Overs.
Earn the true ending.
Complete the game in Flat Legend.
Earn all of the achievements.
Beat 50 Bunny Balls.
Beat 50 Squidclops.
Beat 50 Sparks.
Beat 50 Roundowls.
Beat 500 enemies.
Beat 1000 enemies.