Here is the full list of all 22 99 Levels To Hell achievements.
Found the Dragon
Found all the hidden books
Die 100 times
Beat the Devil
10 hours in the dungeons
Beat the 9th boss
Collect 10.000 gold
Beat the 7th boss
Beat the 8th boss
Used a cheat code
Beat the 4th boss
Beat the 5th boss
Beat the 6th boss
Found the Hunter
5 hours in the dungeons
Beat the 2nd boss
Beat the 3th boss
Found the Major
Spill 1000 liters of blood
2 hours in the dungeons
Beat the 1st boss
Ghost?