Your objective for this achievement is to kill 1986 goblins using the Entropy skill as the killing blow for each one.
First off, you need to have your Dusk Mage be at least level 20 in order to have access to the Entropy skill.
Once you have Entropy, hop over to the Edgewood Bluff level. It’s one of the game’s first areas and it’s filled with low level goblins. Since you’re level 20, your Entropy attacks should kill almost all the goblins in 1-2 casts. Since you’re over-leveled for the area your kills won’t count towards leveling up, but they will count towards profession for the achievement.
Once you’ve cleared the level of enemies just exit to the main menu and then hop back into the same level. All the enemies will have respawned. Grind away!