Here is the full list of all 25 Voidwalkers: The Gates Of Hell achievements.
Kill 50 Zombies
Kill 150 Zombies
Kill 500 Zombies
Kill 1500 Zombies
Kill 5000 Zombies
Kill 5 Bosses
Kill 15 Bosses
Kill 25 Bosses
Kill 50 Bosses
Kill 100 Bosses
Survive 10 Rounds
Survive 100 Rounds
Survive 150 Rounds
Survive 250 Rounds
Survive 300 Rounds
Earn 5000 Points
Earn 7500 Points
Earn 10000 Points
Earn 15000 Points
Earn 50000 Points
Use The Mystery Box 5 Times
Use The Mystery Box 10 Times
Use The Mystery Box 15 Times
Use The Mystery Box 20 Times
Use The Mystery Box 25 Times