Here is the full list of all 21 NeverEnd achievements.
Kill your first enemy
First death
Buy your first item
Kill your first mini boss
Buy all items
Finish the second quest
Kill every mini boss in one run
Collect all hats
Konami code
Beat the game
Complete the game with the stick
Kill the dummy
Find one elemental sword
Walk through 100 rooms in one run
Die in the first 10 seconds
Buy a Bow and a Rod in one run
Kill 50 enemies with the bow
Finish the first quest
Get 20c in one run without the Rod
Walk into a room with 6 Zomborgs
Kill the final Boss