Dealing Magic Damage causes additional damage based on target's health.
When you deal Magic Damage to a player-controlled unit, applies a debuff that deals 4% of target's current Health in Magic Damage per second and reduces health regeneration by 75% for 3 seconds.
Debuff damage is reduced to 33% if you deal DoT damage instead.
Spell Sunder's debuffs do not stack with itself or activate from its own DoT.