If two or more 6s are rolled when casting a spell, it has been cast with irresistible force. The spell will be cast automatically and cannot be dispelled, but the Wizard has to roll on the Miscast table when the spell has been resolved.
Magic is fickle, and writhes like a thing alive even whilst a Wizard shapes it to his will. Magic always strives to be free of constraint, and should the Wizard mispronounce a single word, or otherwise miscast the spell, the magic will shatter its bindings in a burst of incredible energy. Wizards can therefore be described as not trying to empower their spells, but to hold that same energy in check lest it prove to be their undoing.
If a Wizard rolls two or more unmodified 6s when determining his casting result, the spell has been cast with irresistible force. When seeing if irresistible force has occurred, always use the actual dice scores, irrespective of bonuses from special rules or magic items. If a Wizard is called upon to re-roll the dice for any reason, it is the second result that stands, as is normal for a re-roll.
All dice rolled count towards irresistible force, regardless of whether the dice were power pool dice, or granted as a bonus from a special rule or magic item.
For example, a Level 1 Wizard attempts to cast the formidable Life magic spell, The Dwellers Below (casting value 18+) and rolls four dice, scoring 1, 2, 6 and 6 (for a casting total of 15+1 for the Wizard's level). As two 6s were rolled in the casting attempt, the spell is cast with irresistible force – it doesn't matter that the casting total is lower than the spell's casting value.
On the one hand, irresistible force is a good thing, because the unshackling of power ensures that the uncontained raw magic pulses through the Wizard's spell and empowers it in such a manner that it cannot be prevented.
A spell cast with irresistible force automatically succeeds, even if the casting total is not enough to reach the spell's casting value. More importantly, perhaps, a spell cast with irresistible force is impossible to dispel – your opponent cannot even attempt to prevent the magical mayhem soon to be unleashed – go straight to Step 4, Spell Resolution.
However, irresistible force is also a very bad thing indeed. When irresistible force occurs, the wildly arcing magic inevitably proves dangerous to the Wizard and to anyone nearby. Naturally, the Wizard will do his best to contain the uncontrollable energy, but success is by no means guaranteed – this is what we refer to in rules terms as a miscast.