This is a bugged achievement.
Buy a pack in shadow lord and get the Snake Guardian. Equip it and play a match. Use a combo ender and it will poison the opponent. Deal 1500 damage and over time it will pop.
The bug(confirmed by ParadoxReal8):
HOWEVER, the achievement pops almost straight away after you do your first ender.
True! Faster Guardian achievement! Equipped it first against a Omen and it pop almost immediately!