Here is the full list of all 50 Dreamkiller achievements.
Complete a Single Player game in Time Trial mode.
Complete a Single Player game in Single Weapon mode.
Complete Story mode on the Nightmare difficulty.
Complete one level in Story mode while only using the Sunbeam.
Kill 400 Enemies while using the Dragon's Grasp.
Complete one level in Story mode while only using the Dragon's Grasp.
Complete Story mode on the Insanity difficulty.
Kill 400 Enemies while using the Sunbeam.
Die 10 times to self-inflicted explosives fire in any Single Player mode.
Conquer 50 brains in Conquest mode.
Finish a Deathmatch game with the highest score (with at least 3 other players involved).
Kill 3 or more opponents at the same time in a Multiplayer game.
Die 5 times while in the Subconscious.
Kill 25 Enemies while teleporting.
Achieve the Gold weapon upgrade rank on the Insanity difficulty.
Complete Chapter 4 on any difficulty.
Enter Berserker Rage at least once in each level of the game in Story mode.
Complete every level on any difficulty without dying.
Complete every level on any difficulty without dying in the Subconscious.
Complete Story mode on the Bad Dream difficulty.
Use every weapon at least once in any level of the game in Story mode.
Kill 100 Enemies while using the Sunbeam.
Complete one level in Story mode while only using the Hailstorm.
Complete Chapter 3 on any difficulty.
Complete one level in Story mode while only using the Dream Cleaner.
Kill 400 Enemies while using the Dream Cleaner.
Complete one level in Story mode while only using the Minigun.
Kill 100 Enemies while using the Dragon's Grasp.
Complete one level in Story mode while only using Shock Therapy.
Kill 400 Enemies while using Shock Therapy.
Return your team's flag at least 5 times in one CTF match.
Kill 300 opponents in any Multiplayer game mode.
Kill 100 opponents in any Multiplayer game mode.
Enter Berserker Rage during a Multiplayer game.
Kill 25 opponents in any Multiplayer game mode.
Kill 10 opponents in a row without dying in a Multiplayer game.
Complete Chapter 2 on any difficulty.
Kill 100 Enemies while using the Dream Cleaner.
Kill 10 or more enemies at the same time with any weapon.
Defeat a Doorkeeper without taking any damage.
Kill 400 Enemies while using the Minigun.
Kill 100 Enemies while using Shock Therapy.
Complete Chapter 1 on any difficulty.
Defeat a Dreamkiller without taking any damage.
Kill 400 Enemies while using the Hailstorm.
Kill 100 Enemies while using the Hailstorm.
Complete a level on any difficulty without dying.
Complete one level without receiving any Health pickups.
Find and enter in all of the Secret areas in any one level of the game.
Kill 100 Enemies while using the Minigun.