Here is the full list of all 36 Under Spire achievements.
Accumulated 1000 Coins
Accumulated 100 Cards
Accumulated 10 Treasures
Fewer than 10 deck cards at the win
More than 50 cards at the win
Victory below 100 HP
Defeat BOSS by 5 Mana
Defeat BOSS with Full Health
Use the Mage to pass the Normal
Use the Hunter to pass the Normal
Use the Paladin to pass the Normal
Use the WarLock to pass the Normal
Use the (Frost Classic) Deck to pass the Advance 7
Use the (Endless Spell) Deck to pass the Advance 7
Use the (Hand Corps) Deck to pass the Advance 7
Use the (Trap Classic) Deck to pass the Advance 7
Use the (Hoarding Prey) Deck to pass the Advance 7
Use the (Exotic Hunting) Deck to pass the Advance 7
Use the (Heavenly Blessing) Deck to pass the Advance 7
Use the (Soul Knight) Deck to pass the Advance 7
Use the (Mechanical Legion) Deck to pass the Advance 7
Use the (Flame Classic) Deck to pass the Advance 7
Use the (CoolHeart) Deck to pass the Advance 7
Use the (Eternal Legion) Deck to pass the Advance 7
Use the (Frost Classic) Deck to pass the Hard 7
Use the (Endless Spell) Deck to pass the Hard 7
Use the (Hand Corps) Deck to pass the Hard 7
Use the (Trap Classic) Deck to pass the Hard 7
Use the (Hoarding Prey) Deck to pass the Hard 7
Use the (Exotic Hunting) Deck to pass the Hard 7
Use the (Heavenly Blessing) Deck to pass the Hard 7
Use the (Soul Knight) Deck to pass the Hard 7
Use the (Mechanical Legion) Deck to pass the Hard 7
Use the (Flame Classic) Deck to pass the Hard 7
Use the (CoolHeart) Deck to pass the Hard 7
Use the (Eternal Legion) Deck to pass the Hard 7