Here is the full list of all 25 Numgeon achievements.
Destroy Your First Number
Unlock all Color Palettes
Open 100 Treasure Chests
Save the Dragon
Die 100 times
Use Shrine 100 times
Slay the Princess
Drink 100 Potions
Eat 100 Apples or Breads
Make 1000 Combos
Destroy 500 Numbers
Destroy 1000 Numbers
Destroy 5000 Numbers
Destroy 10K Numbers
Destroy 50K Numbers
Destroy 100K Numbers
Finish the game on Expert difficulty
Use Start-Up machine 100x
Use Bonfire 100x
Finish the game with Knight
Finish the game with Sorcerer
Finish the game with Assassin
Use Magic 100x
Visit the shop 100x
Complete 100 Missions