Full list of all 41 Monster Sanctuary achievements worth 1,200 gamerscore. It takes around 40-50 hours to unlock all of the achievements in the base game.
The base game contains 34 achievements worth 1,000 Gamerscore, and there is 1 DLC pack containing 7 achievements worth 200 Gamerscore.
Complete twenty five battles in the Infinity Arena OR PvP
Obtain all monsters
Receive 5 star scores against all Champions
Uncover the whole map
Become a Keeper Master
Defeat Marduk
Beat all of Trainer Gotthelm's challenges
Explore the forbidden catacombs
Enter the Land of Blobs
Prove a worthy opponent
Uncover the source of Marduk's powers
Deal over 10,000 damage in a single hit
Upgrade 50 pieces of gear
Recover long lost treasure
Donate 100 Monsters to the Monster Army
Receive a Tanuki Egg
Achieve at least a 25 x Combo
Obtain a shifted monster
Restore balance to the Sun Palace
Evolve a monster
Defeat the Goblin King
Win 200 wild encounters
Confront the Alchemists in the Library
Become A Keeper Lancer
Pass the Oracle's test
Defeat all monsters in a single turn
Receive a 5 star score in the Champion Challenge
Receive a reward from the Monster Army
Calm the Blue Caves
Help out a resident of the Sanctuary
Complete Old Buran's training
Five-star a battle
Discover a hidden room entrance
Hatch first monster
Tread where no Keeper has gone before
Free the Wanderer from their icy prison
Restore the World Tree and learn about the true form of your Spectral Familiar
Fully equip a Bard with instruments
Reach max level with a Monster
Unlock all alternative outfits
Defeat all Legendary Keeper Battles