The key difficulty with simplifying ArM are the spell guidelines. So - I suggest a unified spell guideline list - and I eliminated Rego, so now the game's even simpler!
General Spell Guidelines
Magnitude 0: Minor effect.
Creo: Make a minor improvement to an item, such as an artisan might make by maintaining it.
Intellego: Discern a single (one word) piece information that can easily be found by cursory inspection.
Muto: Change a minor aspect of the target, such as changing its appearance or color.
Perdo: Do superficial damage, such as a Scar.
Magnitude 1: Small effect.
Creo: Create loose parts, such as dirt or feathers. Fix a broken item.
Intellego: Discern a single piece information that can normally be found by a short examination using an Ability, or basic information (a few words) that can easily be found by cursory inspection.
Muto: Make a small natural change to the target, such as moving it slowly.
Perdo: Inflict a Light Wound.
Magnitude 2: Semi-natural effect.
Creo: Create a basic Individual of Form, such as a bird or fish.
Intellego: Discern a single piece information that can normally only be found by an extensive skilled examination, basic information that can normally be found by a short inspection using an Ability, or brief (a sentence) information that can easily be found by cursory inspection.
Muto: Make a natural change to the target, such as controlling its motions.
Perdo: Inflict a Medium Wound.
Magnitude 3: Basic magical effect.
Creo: Create a major example of the Form, such as a mammal.
Intellego: Discern basic information that can normally only be found by extensive skilled examination, or brief information that can be found by a short use of an Ability, or thorough information (all relevant information) that can be found by cursory inspection.
Muto: Make a slightly unnatural change to a target, such as moving it quickly, teleporting a short distance, making its body resistant to damage (Soak +3), giving it a different creature's natural ability, or changing its Size (+1).
Perdo: Inflict a Heavy Wound.
Magnitude 4: Major magical effect.
Creo: Bring the target to perfection unnaturally, such as making an animal grow to maturity in a short while.
Intellego: Discern brief information that can normally only be found by extensive skilled examination, or thorough information that can be found by a short use of an Ability.
Muto: Turn a target to a different but somewhat-related Form, such as a man into another animal (with Requisites).
Perdo: Inflict an Incapacitating Wound.
Magnitude 6: Great magical effect.
Creo: Create a supernatural exemplar of the Form, such as a Beast of Virtue.
Intellego: Discern thorough information that can normally be found only by extensive skilled examination.
Muto: Turn a target into a completely different Form (with Requisite), such as turning a man into air.
Perdo: Kill a person.
Higher magnitudes are possible, to represent even more supernatural effects.
Add extra magnitudes in spell design as desired. Most commonly: +1 for violent (often - causing +5 more damage than the base effect), +2 for extra-violent, +1 for fine control or intricacy, +1 for more unnatural than base effect, +1 for allowing extra effects (with or without Requisite).
One can use guidelines from another Technique when appropriate. For example, spells should not do more damage than the Perdo guidelines indicate.
Use the standard Individual per Form as in the core book. And of course add magnitudes to affect greater size.
All this does not re-create the core game's spells precisely, but is often close and is simpler than having numerous lists. Individual TeFo lists are still strictly-speaking needed, to give examples of the general ideas (for example - perhaps "a basic Individual of Mentem" is an emotion, whereas a "major example" is a thought or memory). Which I'm sure why this kind of approach wasn't ever used in ArM - if TeFo lists are needed anyway, you might as well just have them. But for this game - well, it's simpler to have one spell guideline list rather that 50.
