Arcana covers knowledge of all things magical that do not deal with metaphysics. In combat, it can be used to increase the power level of scrolls.
Arcana has the following effects:
Determines the maximum level of scrolls that can be used by a character. Unlike Lore in Pillars of Eternity, this is a direct comparison. The required Arcana level is shown on each scroll.
Increases the power level of all used scrolls by Arcana level x 0.5 (or 0.5 per point)
As with all other skills, Arcana can be checked during conversations and scripted interactions.
Scrolls power level
Each power level in scrolls has the following effect (where applicable):
+5% healing done.
+5% duration (some exclusions, such as "per" intervals).
+0.25 Penetration - rounded up to the nearest 0.1, though this may be for display only.
+0.5 bounces - rounded down to nearest integer (truncated). Note that no tooltip is displayed for this bonus.
+1 Accuracy - rounded down to nearest integer (truncated).
So, at 10 Arcana, the power level for scrolls would be 5 (excluding other potential power-level altering factors). At power level 5, the scroll gains +25% damage, +25% duration, +1.25 Penetration, etc. Note that power levels are rounded down to the nearest whole number, so a character with Arcana 3 would add 1.5 power levels to used scrolls, but the calculation will round this down to 1.
Power level scaling can be overridden on a per-item basis, meaning the above bonuses may not apply for every item! These figures are given as a guideline to the power level scaling values of most items.
All bonuses only apply to the scrolls direct effects, so if a scroll were to grant the caster Accuracy (for example), it would not gain an added bonus from power levels. The bonus only applies to the accuracy of attacks made by the scrolls casted ability, likewise with Penetration.
Scroll power level bonuses
Bonuses to scrolls
Damage / Duration / Healing
The above table outlines the bonuses received to scrolls at a specific power level (and in turn Arcana level). This assumes no other factors are influencing the power level for scrolls, but the effects should be the same either way.
The following bonuses are applied as a result of a character's class and background.