Vengeance

Vengeance is a Lunar spell that causes the next damage attack that hits the player casting this spell to also hit the player dealing the damage for up to 75% of the damage originally dealt to the casting player. As with all Lunar Magicks spells, the quest Lunar Diplomacy must be completed to cast this spell. Many melee players use the Lunar Spellbook for this particular spell so they can deal extra damage back to their opponents. Vengeance spells can only be cast once every 30 seconds by the same caster.

Remember, you cannot use normal Magic or Ancient Magicks spells if you are using Lunar Magicks, except by use of the Spell Book Swap spell.

Trivia
The Vengeance Bug caused players having the Vengeance Spell remaining to knockout (kill within one hit) any monster. A screenshot has been proving an unnamed player to hit 190 on King Black Dragon.