In Ars Magica, a magi may counter incoming spells and effects:
In order to create a fast-cast defense against magic, a maga must know the Hermetic Form that governs that magic. If the caster is a Hermetic maga and is using words and gestures that she can hear and see, she may determine this automatically. ... In general, a fast-cast defense with half the level of the attacking spell is enough to protect the maga herself or one other individ- ual. The spell still takes effect, and the side effects of deflecting the spell may have to be dealt with. A fast-cast defense that matches or exceeds the level of the attacking spell can completely neutralize it, probably in a fairly spectacular fashion.
Are there any guidelines as to what, exactly, constitutes a counter?
Specifically, I am building a Villain (effectively Dr. No) who is built around countering incoming spells. He plans to use the fast-cast spell mastery:
The maga may Fast Cast the mastered spell according to the rules for Fast Casting Spontaneous spells, on page 83. The maga still takes the –10 penalty to Casting Score and risks the extra botch dice, although the botch dice will be partially offset by her Mastery Ability.
Along with a number of formulaic spells to shut down incoming magic.
What set of formulaic spells does he need in order to deal with almost all incoming magic? In a more general sense, are there guidelines for appropriate spontaneous spells?