Here is the full list of all 46 Deep Dungeons of Doom achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
Buy all Crusader skills
Buy all Mercenary skills
Buy a level 6 skill with the Crusader
Buy all Witch skills
Drink poison and die
Causing more than 100 points of damage in one hit
Find 10 secrets
Buy a level 6 skill with the Witch
Collect 10000 gold
Reach the floor 666 on DDD
Reach the floor 360 on DDD
Reach the floor 300 on DDD
Reach the floor 260 on DDD
Reach the floor 200 on DDD
Reach the floor 160 on DDD
Reach the floor 100 on DDD
Reach the floor 60 on DDD
Find 6 secrets
Buy a level 6 skill with the Mercenary
Kill 1000 monsters
Reach the floor 30 on DDD
Reach the floor 10 on DDD
Clear the Deepest Dungeons of Doom
Collect 5000 gold
Use a revive
Find 3 secrets
Taking more than 20 points of damage in one fight
Kill 50 beast monsters
Slay the Icy Caves' boss while carrying no equipment
Find one secret
Completing a dungeon with 1 hp
Kill 50 undead monsters
Die in a single hit with full health
Kill 50 human monsters
Collect 1000 gold
Kill 100 monsters
Collect 500 gold
Clear 6 dungeons
Collect 300 gold
Die on a dungeon first floor
Clear 3 dungeons
Use a revenge bonus
Die for the first time
Kill a zombie
Clear the Sewer
Completing a dungeon without using any potions