Fortress

If you have the following: Units that can use this synergy:
 * 2 Units: With every attack, Fortress units have 20% chance of stunning their enemy for 1.5 seconds.
 * 4 Units: With every attack, Fortress units have 35% chance of stunning their enemy for 1.5 seconds.
 * Rune Priest.
 * Battle Dwarf.
 * Valkyrie.
 * Lave Elemental.
 * Fire Giant.
 * Red Dragon.