Here is the full list of all 55 Ancient Dungeon achievements.
Defeat a Mad Merchant.
Escape The Ancient Dungeon after re-entering once.
Consume a food item made of gold.
Open 250 chests
Challenge and destroy a boss with only a half-heart of health
Defeat one hundred aberrant enemies.
Destroy a Sacrifice Statue.
Carry more than two hundred fifty coins during a single delve.
Acquire more than five full hearts of health.
Defeat a Chest Mimic.
Traverse The Infested Dungeon without taking any damage.
Traverse The Forgotten Library without taking any damage.
Traverse The Beast's Cradle without taking any damage.
Damage The Beast with the Assassin's Armament.
Discover a secret room in the ceiling.
Defeat a boss enemy with a single strike.
Traverse The Overgrown Gatehouse without taking any damage.
Traverse The Luminous Mines without taking any damage.
Strike enemies with a ranged weapon twenty-five times in a row without missing.
Acquire three highly powerful items during a single delve.
Explore two hundred fifty rooms within The Ancient Dungeon.
Damage The Beast with the Mercenary's Armament.
Acquire four items from shops during a single delve.
Deal at least twenty-five damage with a single strike.
Discover a secret room in the wall.
Carry more than twenty keys during a single delve.
Damage The Beast for the first time.
Defeat a Possessed Armor.
Use The Blacksmith's Anvil to augment a weapon.
Enter The Ancient Dungeon for the first time.
Overcome a Challenge Chest's trial.
Use a Bandit Box at least twenty times during a single delve.
Raise your merchant discount to 60%.
Destroy one thousand pots.
Discover (almost) all items.
Escape The Ancient Dungeon without consuming any food items.
Use a Contracting Orb to shrink yourself.
Win big on The Merchant's slot machine.
Eat every type of food item during a single delve.
Defeat a Golden Slime.
Escape the dungeon without obtaining any upgrade items.
Escape The Ancient Dungeon after re-entering three times.
Escape The Ancient Dungeon after re-entering twice.
Lower your merchant discount to -100%.
Damage The Beast with the Mercenary's Armament in hard mode.
Damage The Beast with the Assassin's Armament in Hard Mode
Escape the Ancient Dungeon without entering a shop.
Escape the Ancient Dungeon in under twenty minutes.
Fully augment the Assassin's Armament.
Fully augment the Mercenary's Armament.
Throw a dragonfruit into a pit.
Complete the delve of every Sealed Soul.
Complete 3 unique sealed soul delves
Escape The Ancient Dungeon with a difficulty modifier of 2.25
Escape The Ancient Dungeon with a difficulty modifier of 3.00