Remnant of Corruption (debuff)
You are slowed and taking Physical Damage over time
Takes 6% of Maximum Life as Physical Damage per secondTakes 6% of Maximum Energy Shield as Physical Damage per second
30% reduced Movement Speed
Remnant of Corruption is a monster aura. It applies a debuff to nearby enemies that inflicts physical damage over time and reduces their movement speed. It's area of effect is fairly small and can be avoided by staying outside of melee range with the monster.
Sources
The Remnant of Corruption aura is used by rare monsters trapped in essence crystals that appear with a 
Remnant of CorruptionRemnant of CorruptionStack Size: 9Corrupts the Essences trapping a monster, modifying them unpredictably
Right click this item then left click a monster trapped by Essences to corrupt them. Corrupted Essences cannot be modified again.
on them. When broken free from the crystals, a rare monster with the Remnant of Corruption essence will use this aura. (See Remnant of Corruption for more details about this encounter.)