Here is the full list of all 20 Dead Dungeon achievements.
Use the portal
Complete 10 levels
Die for the first time
Find first collectable
Kill the first enemy
Die 100 times
Die 500 times
Die 1000 times
Collect all donuts
Collect all collectables
Kill 100 enemies
Activate the trap
Find the first secret level
Find the second secret level
Kill the enemy in an unexpected way
View credits
Complete 20 levels
Complete 30 levels
Complete 40 levels
Defeat the boss