The Dreaded Thirteenth Spell

 is a unique spell ability for Grey Seers. It summons a unit for Stormvermin (Halberds) to the battlefield.

Since it is a unique spell, it is technically not a part of either the Skaven Spells of Plague or Skaven Spells of Ruin.

Description
The Curse of the Horned Rat is the dreaded 13th spell - the fabric of reality is torn and the Horned One’s children spill forth!

Effect

 * Type: Explosion
 * Duration: 13 Seconds
 * Cost: 20 Winds of Magic
 * Cooldown: 52 Seconds
 * Target: Ground, enemy 200m
 * Summons a unit of Stormvermin (Sword & Shield)
 * Huge explosion area
 * Can disrupt unit formation
 * Strong vs. multiple units
 * Summoned units degrade over time