Arcanum: Of Steamworks and Magick Obscura Wiki
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Spell Resistance Certain spells will check a specific primary statistic of their target and roll for a "saving throw" before any effect takes place. Generally, these statistics are either Constitution (CN) or Willpower (WP). For example, a spell resisted by CN will roll for a number between 1 to 20, and if the target's CN is equal to or less than the result, the spell will be resisted in some way (i.e. halved damage or no effect). It is uncertain if having a statistic over 20 (e.g. because of racial modifiers) affects saving throws in any way.

Rolls for saving throws will often have additional modifiers that either benefit the target or the caster. Generally, a positive modifier goes to the benefit of the target, while a negative modifier goes to the benefit of the caster. A spell resisted by CN+10 will be resisted far more often than a spell resisted by CN-5. Detailed examples of saving throws involving modifiers can be found below.

Magic Resistance (MR) acts before any saving throws are made. MR makes it harder for a creature to be harmed by damage-dealing spells, but also harder to be healed by healing spells.

MR has four possible effects/results depending on the spell being cast:

  1. Damage causing spells have their damage reduced by the amount of the target's magic resistance.
  2. Sustained spells have their sustainment fatigue cost increased by the factor 100/(100-resistance) and cannot be maintained on 100% resistant creature
  3. If a spell does not deal damage, but has a "saving throw", target receives +1 bonus on the save for each 10% of res. (+1 for 1-10%, +2 for 11-20%, etc. up to +10 for 91-100%)
  4. The spell may fail to cast at all based on chance equal to target's mag. res.

How certain spells may be affected by MR:

  1. Fireflash on cr. with 80% mag res will only deal 20% of intended damage
  2. Shield of prot. will cost more FT/s on that cr.
  3. Charm is resisted by the same cr. at +8 to its saving throw
  4. Unseen force has an 80% chance to fail to push the creature at all

Here's a simple example of rolling for a saving throw where the target has no magic resistance:

  1. A spell resisted by CN-5 is cast upon a creature with 8 CN
  2. The creature's CN is reduced by 5 for purposes of deciding a saving throw and is now 3
  3. The game rolls for a number between 1 to 20 — if the number result is 3 or less, the spell is resisted

And here's a complex example with magic resistance as part of the equation:

  1. A spell resisted by CN-5 is cast upon a creature with 12 CN and 10% magic resistance
  2. The creature's CN is reduced by 5 for purposes of deciding a saving throw and is now 7
  3. The creature's CN is increased by 1 due to its magic resistance and is now 8
  4. The game rolls for a number between 1 to 20 — if the number result is 8 or less, the spell is resisted
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