Nature

A strike plus poison: the slowest damage-over-time in the game, and the only one that also cuts the target's healing for as long as it lasts. Against anything that sustains itself the heal reduction is usually worth more than the damage, and nature legendaries push that reduction high enough to effectively delete an enemy's regeneration.

Power scales the strike, the tier-6 aura and the tier-9 signature both deepen the heal cut, and proc gains raise how often the poison lands.

Anything that heals - world bosses, sustain builds in the arena, and the several dungeon bosses whose whole plan is outlasting you.