Rego Terram acts as the default form for moving miscellaneous items around, and destroying small things of all forms is almost as handy – so this spell is Perdo utility spell for generic destruction.
The intent is to design a spell which is usable as a more generic defense spell which could then be Mastered and fast cast. I’d argue this effect is no more of a rort than The Unseen Arm (Ars Magica page 155).
Perdo Terram 25, R: Voice, D:Momentary, T: Part
A miscellaneous object or substance is destroyed by this effect, or if the object is larger than its standard size the caster can destroy part of the item.
Casting requisites are required for non-Terram substances. Complexity in design allows for destruction of more than the base material type in each substance. E.g. metals are effects within Terram.
(Base 3 for destruction of earth, +2 for more complex materials such including metal Terram, +2 Voice, +1 Part, +1 flexibility in approach)
I can see a generic destruction effect being controversial as it might replace spells for specific forms. The real problem was deciding what the base effect level might be and if additional mags were needed for the general approach. I decided to add additional magnitudes to reflect both. This is a very desirable spell for a Perdo specialist who can then master one effect instead of many – thus it might break the first rule.
This and around 395 other new spells for Ars Magica can be found here.