The achievement will pop up when you equip Death with Elite items (purple border weapons and items). Once you equip primary weapon, secondary weapon, chest, hands, legs and talisman with purple border items (elite items), the achievement will be unlocked.
Elite items can be found randomly or you can buy them to Vulgrim and the other seller in the game. If you don't find any elite items (the border and letters are purple colored) in the sellers inventory, you can retry later as the selling items respawn. These items could be less useful than others, so just equip them to unlock the achievement.