Vengeance

Vengeance is a Lunar Spell that rebounds 75% of the damage of the next hit back to their opponent, similar to a ring of recoil or deflect curses. However, this effect will wear off after half an hour. Some monsters are immune to it, however. To activate it, one must incantate "Taste Vengeance!" Upon being activated, a giant pink skull will come down and engulf the caster's opponent.

Vengeance first appeared in While Guthix Sleeps, during the Castle War between the Varrockians and Zamorakians. Instead of casting Vengeance on Aidan, Zamorak casted it upon the Tormented Demon he had summoned. For a moment, the skull had completely devoured it and the Demon had disappeared. It then came back from thin air, roaring with immense power.

The next instance of Vengeance was in the Woods of Holly. Zamorak had casted the spell onto King Roald, but before the skull had time to swallow the former king, Roald had demolished the skull, his Master wand pointed toward the sky. The destruction of the skull was so intense that it cracked the wand down the middle, despite Master wands being the most powerful wand.

Trivia

 * The effects of Vengeance in the novels seem to differ from the effects in the game. In While Guthix Sleeps, Zamorak casted it onto his Demon, which wouldn't make sense in the game, considering the Tormented Demon was Zamorak's, to some extent, familiar, and not his opponent. It instead made the Demon twice its normal size and extremely more powerful. The next time he had cast it was in the Woods of Holly, and even then, the effects seemed to differ. Zamorak did cast it onto his opponent, but from Zamorak's remark, it seemed as though Vengeance just heightens the power of the caster's next spell, not deflect the opponent's spell back onto himself. However, being an immensely powerful dark god, it's possible Zamorak altered the spell, or it's just a different form of Vengeance entirely.