Here is the full list of all 30 Caverns of the Snow Witch achievements.
Find the ultimate ending in Hardcore mode
Find all enemies with these words in their name
Survive being swept up by an avalanche
Find the ultimate ending in Medium mode
Survive your own murderous hand
Find all the images hidden within Caverns of the Snow Witch
Steal a boat and sail away
Steal a meal of duck
Find the ultimate ending in Free Read mode
Fly on a Pegasus
Successfully navigate your way past the Banshee
Convince the centaurs that you have nothing of value
Beat the Snow Witch at her own game
Slay the zombie replicas of your friends
Experience a particularly nasty shower
Read the spell on the scroll before it fades away
Find all three metal shapes
Consume ten of your Provisions
Deny the Brain Slayer of a meal
Take all of the Snow Witch's treasure
The Snow Witch is Dead!
Remember an old legend to your benefit
Shatter the Crystal Warrior into pieces
Try all three of the rings
Hit the true Illusionist on your first try
Receive a curse from a stranded Dwarf
Be healed by the minstrel's music
Solve the riddle of the rhyme
Trick two foolish Goblins
...even if it's not your birthday