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