Here is the full list of all 15 Ittle Dew achievements. It takes around 8-10 hours to unlock all of the achievements on Windows.
Complete the game with all three items
Defeat an off-screen enemy
Discover a shortcut in an item dungeon
Launch a Pancake enemy into the air
Complete the game with only Fire sword and Ice wand
Complete the game with only Portal wand and Ice wand
Complete the game with only Fire sword and Portal wand
Complete the game in less than 15 minutes
Complete the game in less than three hours
Complete the game without harming any Frog, Fox, Berry or Deer Jennys
Find every card
Find every piece of paper
Teleport a flying axe so that it hits you anyway
Complete the Master Cave
Complete the Compost Crypt