Child of the EarthG 15

The easiest way to get this achievement is to equip the Mesa Valorplate and use its Archon's Fury, but you can combine this with a weapon that a high poison percentage chance. You can also add/ increase the chances and damages with charms, lifestones, rings, etc... (Watch for anything that says poison or Earth)

Achievements for this game don't track on Xbox, but you can track this achievements in the in game "Merits" tab in the menu under the "Child of the Earth" Merit. Once you reach 100 total enemies, the achievement will pop.