Here is the full list of all 48 Flat Kingdom achievements.
Complete the game in Flat Newbie.
Complete the game in Flat Hero.
Earn the normal ending.
Defeat the last boss.
Get 100% coins in Flatelysium.
Activate the last Checkpoint Guard.
Get the final journal page.
Defeat Hex.
Open the path to the sky tower.
Get 100% coins in Flatlantis.
Beat 50 Squidclops.
Get all the special abilities.
Defeat Fenrir.
Defeat the Norns.
Defeat Flatepetl.
Get all the coins.
Defeat Quetzal.
Change your shape 1000 times.
Buy your first heart from the store.
Get your first special ability.
Defeat Kraken.
Defeat Hank.
Defeat Arachne.
Get 1 Game Over.
Defeat Plantosaurus.
Defeat an enemy with two or more shapes.
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 Flatepetl.
Get 100% coins in Flatsgard.
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 Sparks.
Beat 50 Roundowls.
Beat 500 enemies.
Beat 1000 enemies.