The easiest way to get this achievement is to equip the Phoenix Valorplate and use its Archon's Fury, but you can combine this with a weapon that a high Ignite percentage chance. You can also add/ increase the chances and damages with charms, lifestones, rings, etc...
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 "Disciple of Alaz" Merit. Once you reach 100 total enemies, the achievement will pop.