Magic Resistance: Revised Rules

The intent behind these revised rules is to make Ars Magica magic resistance less all-or-nothing. Lots of small spells should be something of a threat, while a single big one should not have no effect at one level, and be instant death one level higher. In addition, the Parma Magica should be a major discovery, that revolutionises magical protection.

The Resistance Roll

All magical creatures get a resistance roll against any spell or magical effect that tries to affect them. Magi roll stress die + Form/5, creatures with Might roll stress die + Might/5. The spell rolls stress die + level/5 + caster's Penetration Talent. If the target rolls higher, the spell fails to affect him. If he rolls lower, or there is a tie, the spell does affect him. If the spell botches, it fails to affect the target, regardless of relative totals, and if the target botches, it is affected, again regardless of relative totals.

Note that the spell bonus is based on the level of the spell, not its penetration.

Things and characters with no magic resistance do not get to make this roll.

Parma Magica

The Parma Magica allows magi to create a number of magical shells around themselves.The magus may create any number of shells, up to his Parma score. Each shell may have a level of up to Parma x 5, so long as the total level of all shells is less than or equal to Parma x 10.

When a spell impacts on a shell, it will pass through only if its penetration is greater than the level of the shell. If it does pass through, its penetration is reduced by the level of the shell, and this penetration is compared to the level of the next shell in. If the penetration of the spell is more than twice the level of the shell, the shell is knocked down.

If the spell passes through all the shells, the magus must make a resistance roll, as above, but with a bonus equal to the number of shells through which the spell passed, even if it knocked them down on the way.

If more than one spell strikes a shell in a single round, total their penetrations for the purposes of determining whether the shell is destroyed. The individual spells only pass through if their own penetration is greater than the level of the shell, and each spell that does pass through has the level of the shell subtracted from its penetration.

A magus will know immediately if any shells are knocked down. Shells may be rebuilt at a rate of Parma points per round, up to the normal maximum. A magus may cast spells at the same time on an Int + Conc roll of 12+.

A magus may also create shells around other people or things (Individual Target only), if he is touching them. These shells count towards the same totals, and are subject to the same restrictions, as those around the magus himself. If the other person has no intrinsic magic resistance, they get a resistance roll with a +1 bonus per shell against any spell that passes through the shell. Once all the shells have been destroyed, they get no roll. Once the shell has been raised, the character need no longer touch the magus.

All shells dissolve at sunrise and sunset, and it takes ten rounds to raise them again, as described above.

Note that Parma gives guaranteed protection against spells of low penetration, something which the resistance roll can never give. It should not be possible for non-Hermetic magical traditions to duplicate the shells or this effect, because this was Bonisagus's great breakthrough.

Rego Vim

It is possible to duplicate the effects of the Parma Magica with Rego Vim, but it is not as effective, or as flexible.

A Rego Vim spell creates a single shell. The level of this shell is set at the time that the spell is created. The level of the spell, however, is equal to the total level of shells that can be cast on one person, while maintaining the shell created by this spell. Further, the maximum number of shells is equal to the spell level divided by ten. If spells of different levels are used by one magus, base the limits on the lowest level.

Thus, a ReVi 10 spell could create a single shell of level 10, but it would not be possible to put any other shells around the character. A ReVi 60 spell that created a level 10 shell could be cast six times to put six shells around a character.

This level assumes a Range of Personal, a Duration of Sun, and a Target of Individual.

These Rego Vim spells are compatible with Parma Magica, and do not count towards the total number of levels that the Parma can create. The Parma's shells do, however, count towards the total number of levels that the spell can coexist with. Further, all the Parma shells must either be inside or outside the spell's shell (although the Parma shells could be sandwiched between shells created by two ReVi spells, or two castings of the same spell).

A magus will not know automatically if a ReVi shell is destroyed, and can only raise it by recasting the spell.

ReVi spells may also duplicate the effects of the Form bonus. Such spells give a bonus equal to level/5 to the resistance roll (RDT as for the Parma substitute). If one of these spells is cast on a magus, the ReVi bonus replaces the Form bonus for all Arts, irrespective of which is higher. If cast on a magical creature, the spell replaces the Might resistance. Yes, this can be used as a subtle sort of attack, especially on magi with poor Vim but amazingly good scores in other Forms...

Aegis of the Hearth works more-or-less as in ArM4. The spell resistance aspect, however, functions as, effectively, a single shell that cannot be knocked down. All spells that pass through it have their penetrations reduced by the level of the Aegis, and the shell provides a bonus of +1 to all resistance rolls. This means that characters and objects within the Aegis get a roll, even if they do not normally have any magic resistance. Note that this only applies to spells cast from outside the Aegis. Magi would love to know how Notatus managed to create an indestructible shell, and would love even more to do it on a personal level.

Perdo Vim

It is possible to cast Perdo Vim spells with the deliberate intention of knocking down shells. Such spells must be specifically designed to do this, and will affect both Parma and ReVi shells. The spell will knock down any shell that it strikes, if the level of the shell is less than or equal to the level of the spell. It need not penetrate the shell to knock it down, and its penetration will be reduced in the normal fashion as it passes through shells. If the penetration of the spell is less than the level of a shell, but its level is higher, the shell will be knocked down, but the spell will go no further. These spells can pass through shells without destroying them, and can destroy shells by having penetration greater than twice the level, even if the level of the spell is less than the level of the shell. These spells can knock down Aeges, if invented with a high enough Target, but only by exceeding the level of the Aegis. (Range Near, Duration Momentary, Target Individual)

Creo Vim

A Creo Vim spell may be used to give another spell a higher effective level for the Resistance Roll. This spell must be cast simultaneously with the spell to be boosted (Int + Conc roll of 6+, because this is what the spell was designed for), and the level of the CrVi spell replaces the level of the other spell in the resistance roll. The effective penetration of the other spell is also equal to the penetration of the CrVi spell, which envelopes it.

Note that a magus may cast these spells with spells of a higher level. If his CrVi penetration is higher than his penetration with the other Arts, he gets the benefit of the increased Penetration, but the resistance roll will still be based on the CrVi spell, and will thus be lower than it would have been.