Here is the full list of all 38 Iron Crypticle achievements.
Defeat A Boss In All Its Incarnations
Defeat 3 Types Of Miniboss
Defeat A Boss Without Using A Weapon Pickup
View 20 Item Descriptions In The Ledger
Defeat The Phantom
Defeat Madame Tentacles
Find The Golden Kitty
Finish A Regular Room Without Using A Weapon Pickup
Complete 10 Waves In Endless Mode
Defeat Hexapod
Use The Atomic Fist 20 Times
Collect 1000 points worth of coins
Use 10 Different Weapon Types
Collect 1000 Food Items (Increasing Score Type)
Defeat A Boss Without Taking Any Damage
Buy 10 Items In A Shop
Clear 50 Rooms Of Monsters
Collect 30 Lemons In A Single Game
Use 5 Different Scroll Types
Destroy A Fire Bug
Complete The Mud Pits
Complete An Infestation Room
Get Rainbow Power
Get 100 100x8s In A Single Game
Collect All BONUS Letters
Defeat Gnasher
Pick Up 10 Hearts In A Single-Player Game Session
Collect Or Buy 5 Stat Increases In A Single Game
Complete Castle Crushers 3 times
Defeat The Giant Peepwort
Defeat 1000 Monsters
Complete The First Floor On Hard Difficulty
Defeat Boulderface
Complete The Graveyard
Get The Golden Poop
Find A Map
Complete The Catacombs
Finish A Non-Boss, Non-Empty Room Without Taking Damage