Here is the full list of all 32 Beastmancer achievements.
Finish the game with the permadeath option enabled.
Defeat Memnon
Find every recipe in a single game.
Defeat Circe
Become lord of the Erimune islands.
Spare all your rivals in a single game.
Finish the game with your starter monster alive.
Finish the game by destroying the Portal.
Defeat the Wild Walker
Defeat Alexius
Defeat Paulina.
Defeat Marius
Win a battle using only the 3 Noctua variants.
Win a battle using only the 4 Testudo variants.
Capture at least one of every monster in a single game.
Capture all six legendary monsters.
Depetrify all petrified monsters in the islands.
Defeat the White Lioness
Reach level 20 with a common monster.
Reach level 20 with a unique monster.
Reach level 20 with a rare monster.
Learn every spell in a single game.
Use the Cursed Grimoire to summon a powerful monster.
Reach level 20 with your character.
Defeat Diomedes
Defeat Lady Aurelia
Defeat the Hooded Man
Win 100 battles.
Defeat 1st Warlock Myr
Defeat Nero outside the Arena.
Win 20 battles.
Train at the small island during the Prologue