Source-Limited Bonuses (3.5e Variant Rule)

Source-Limited Bonuses
Because D&D 3.5e has boatloads of material, little of which was designed with the rest of the material in mind, there are a lot of ways to get astronomical bonuses that were never intended to occur. This rule attempts to fix this problem by working under the assumption that most designers had at least vaguely the same idea of what a class feature should do, what a feat should do, etc., but failed to consider how their class interacted with other classes, how their feat interacted with other feats, etc. If this theory holds true, then preventing stacking from similar sources should eliminate most unintended stacking while retaining most intended stacking.

How it Works
Bonus types are now mostly meaningless. Two insight bonuses might stack, and two untyped bonuses might not. Bonus types are usually only meaningful when they apply conditionally (dodge, shield, etc.). Disregard all standard rules on when bonuses do and do not stack.

Instead, bonuses can only stack if they come from different categories of effects; only one bonus from each category may apply. The categories are as follows, given in order of precedence; if a bonus falls into more than one category (e.g., a bonus feat given by a class), it is considered to only be within the first applicable category:
 * 1) Ability Score Modifier: This category includes any time an ability modifier is applied to something. Unlike the other categories, up to two bonuses from this category may be applied.
 * 2) Base Bonus: This category includes Base Attack Bonuses and Base Save Bonuses. Note that a Fighter 3/Paladin 2 has a single BAB (+5) derived from his class progression; however if he gets two different abilities that allow him to apply his BAB to damage, for example, only one applies.
 * 3) Level Dependent: This category includes any bonus that scales with character level, class level, caster level, HD, CR, or any similar metric.
 * 4) Armor: This category includes any armor bonus.
 * 5) Shield: This category includes any shield bonus.
 * 6) Feat: This category includes any bonus deriving from a feat.
 * 7) Racial Trait: This category includes any bonus deriving from the character's race.
 * 8) Class Feature: This category includes any bonus deriving from a class feature, including spells and powers (even spells and powers cast/manifested by another character).
 * 9) Miscellaneous: This category includes any bonus which does not fall into any of the above categories (such as synergy bonuses and item bonuses).

An Exception
Whenever a bonus source specifies that it stacks with some other bonus, the two bonuses do indeed stack even if they fall into the same category.