Tip of the week: Spell Resistance

Spell resistance is not a spell in itself, but an ability possessed by many magical creatures which makes them difficult to affect with magic. It is mainly possessed by Outsiders (i.e. Demons, Devils, Angels and the like) and some creatures from the Underdark (the hidden caverns deep below the earth).

The process of casting a spell on a creature with no spell resistance is resolved in 3 steps:

1. The spell-caster rolls their spellcraft skill check (2d10+ spellcraft skill) to determine how hard their spell is to resist
2. The target makes a saving throw against the spell. The type of save depends on the spell, but is always resolved by rolling 2d10 + saving throw bonus. If the result is higher than the casters' spellcraft check, then the spell is resisted and has none or partial effect (depending on what the spell is
3. The spellcaster determines the effect (rolling for damage, etc.)

For some spells, such as shocking grasp, the spellcaster must make a touch attack roll (this is step 1), and there is no saving throw.

If, however, the target has Spell Resistance, the spell caster must overcome the spell resistance before their spell can affect the target. This spell resistance check is made before the spellcraft check, since if the spell caster cannot overcome spell resistance the spellcraft check is unnecessary. This additional check is called the spell penetration check.

To perform a spell penetration check, one must roll 2d10 and add the spell-caster's level. For example, a 5th level mage rolls 2d10+5. The result must be higher than the target's spell resistance value. Typical values are:

Angels: 17+
Demons: 17+
Dark Elves: 11 + class level
Mindflayers: 25
Deep Gnomes: 11+ class level
Githyanki: 5+ class level

Creatures with spell resistance usually also have powerful magical abilities of their own.

The main methods for defeating spell resistance are:

1. Choose the Spell Penetration and Greater Spell Penetration feats, which add 2 to your level when making the roll to overcome spell resistance.
2. Use abilities (such as Inspire Greatness) which add to your own level, so that you act at higher level when making a spell penetration check.
3. Use abilities (such as are available to the Sublime Chord character) which lower the target's spell resistance, making it easier to penetrate.
4. Find magic items (such as ioun stones) which enhance your spellcaster level
   

It is unlikely that many enhancements to the spell penetration roll will be easily found by a single character. Note also some spells can grant the spell caster spell resistance, a very useful power.

It is important to remember that sometimes a spell fails to affect a creature for reasons other than spell resistance. Fire spells, for example, always fail to affect creatures made of fire. No amount of repeated attempts to use such a spell on a creature of fire will ever make the spell work; but repeated castings of a spell on a spell resistant creature will eventually affect it.