ASFC in % and categories

[Sir_Thaddeus]

As we all know, arcane spells suffer from Arcane Spell Failure Chance if cast in armor. There are ways around this, of course. Several classes, such as the Duskblade, the Warmage, and the Bard, among others, are able to ignore the failure chance in certain categories of armor - being able to cast in all Light Armor, or all Medium or Light Armor, for example. This can be extended by options such as the Battle Caster feat (Complete Arcane) or making your armor out of Mithril. Other classes are able to ignore the failure chance in percentages of chance - the Spellsword and the Suel Arcanomach come to mind. Mithril again, as well as the Twilight enchantment, extend this.
My question for the Playground is, how do these two modes interact? What happens when a Bard wears non-mithril Twilight medium armor, for example? What happens when a Spellsword takes the Battle Caster feat?

[erikun]

The Bard, Duskblade, and other similar classes outright ignore ASF when wearing the appropriate armor. (Base classes typically only do so with their own spells.) A Bard wearing light armor does not suffer any ASF, regardless of how large it is. Even if thee was a light armor with 95% ASF, the Bard casting Bard spells would not be suject to the ASF from the armor.

Abilities that reduce the ASF% do so with any armor worn, and will specify if it only does so for specific armors. For example, a 1st level Spellsword PrC ignores 10% of the ASF of any armor worn. This is specifically stated in the ability to reduce the existing ASF, so a Wizard/Spellsword wearing Cloth Armor takes 0% ASF. A Wizard/Spellsword in Full Plate has 25%.

ASF% reducers generally stack with each other, as they all come from separate sources and are separate abilities. I don't know of any such abilities that overlap and don't stack - the closest I can think of is that higher-level abilities of a class overwrite (do not stack with) lower-level abilities of that same class. A 9th level Spellsword has a total of -30% ASF, not -60% ASF. (You take the highest amount. You don't add the -10% with the -20% and the -30%.)

A Wizard/Spellsword 9 with Mithral Full Plate would have 0% ASF. The Mithral Full Plate would only have 25% ASF (Mithral reducing the Full Plate by -10%) and the Spellsword levels would grant -30%, reducing it down to 0%.

The two abilities do not interact at all with each other. A Bard/Spellsword would not suffer ASF in any light armor, at all, because Bards never suffer ASF when casting their spells in light armor. A Bard/Spellsword 9 in Full Plate would suffer 5% ASF, just like a Wizard/Spellsword 9, for exactly the same reason: Full Plate has 35% ASF, and Spellsword 9 reduces that by -30%.


[EDIT] For clarity:

What happens when a Bard wears non-mithril Twilight medium armor, for example? What happens when a Spellsword takes the Battle Caster feat?
Twilight Breastplate (a medium armor) has an ASF of 15%. A Bard wearing it would have an ASF of 15%. The Bard gets a benefit from wearing light armor, nothing from medium.

A Wizard/Spellsword does not have the ability to ignore spell failure chance from armor, and so they do not qualify for the Battle Caster feat. They cannot make use of the feat even if they had it, because they do not have an ability to ignore spell failure chance to improve upon.

A Bard/Spellsword with the Battle Caster feat would ignore the ASF when wearing light and medium armor. (A Bard without the Spellsword PrC would have the same ability.) The Spellsword reducting in ASF% would only end up applying when the character is wearing heavy armor.

[Sir_Thaddeus]

Alright, thank you. I suspected the two types of ignoring ASF did not interact, but was not certain. So in the sidebar in PH2, when WotC stated that Twilight armor was particularly useful for Duskblades, they were mistaken, I suppose.