Updated 04-05-2016 01:20 AM
To unlock this achievement you simply need to kill 1000 undead creatures in the game. There are plenty of undead once you reach the Neverdeath region of the game. There is no real need to grind it out as this achievement unlocked naturally for me as I was completing quests and leveled up to 30. You can also check your status by bringing up the menu, tab over to Quests, access the journal menu, tab once more to achievements, and scroll down to Slayer.