Wizard(X) Models with this special rule may cast one spell at any point during their activation before attacking.
To cast a spell pick one from the wizard’s army list, pick a target in line of sight, and roll D6+X. If the result is equal to or higher than the number in brackets then you may resolve the spell’s effects.
Enemy wizards within 18” and line of sight may also roll D6+X at the same time, and if the result is higher than that of the casting wizard, then the spell’s effects are blocked instead.
Note that a wizard may only either try to cast a spell or try to block a spell each round.