Fixing Multiclassing in Pathfinder/3.x

Instead of fixing the underlying issues of character multi-classing, Paizo has instead chosen to introduce hybrid classes (Magus, Arcanist, Bloodrager, etc.)--ignoring the issue and adding needless complication to an already complex rules system.  In my Nefret campaign, I am not permitting the use of hybrid classes; instead, I am encouraging characters to pursue multi-classing in order to achieve prestige classes (such as Arcane Trickster, Eldritch Knight, or Mystic Theurge).

The biggest drawback of 3.x muticlassing (which is similar to dual classing of previous editions) is that the system is based on the premise that characters receive an equal power jump at each level.  However, while each hit die and related increases are relatively uniform, class abilities at each successive level are considerably more powerful. For instance, gaining access to a new 4th level spell is certainly more of a benefit than gaining access to a new 2nd level spell.  Therefore, the idea of "class level" needs to be considered in two parts:  class hit die and class ability level.

When gaining a new level, there are three basic steps that a character should follow:

1. Add all features gained by adding a character level (feat, ability modifiers) 
2. Add all features gained by adding a class hit die (hit points, skill points, base attack bonus, saving throw bonuses, and caster level) for your chosen class
3. Determine the class ability level of each trained class and apply all gained features (all other class abilities, including spells known and spells per day)

Step three requires one of the following methods:

XP Per Level Method

Character Level	Experience Point Total			Relative XP per Character Level
	Slow	Medium	Fast	Slow	Medium	Fast
1st	—	—	—	—	—	—
2nd	3,000	2,000	1,300	1,500	1,000	650
3rd	7,500	5,000	3,300	2,500	1,667	1,100
4th	14,000	9,000	6,000	3,500	2,250	1,500
5th	23,000	15,000	10,000	4,600	3,000	2,000
6th	35,000	23,000	15,000	5,833	3,833	2,500
7th	53,000	35,000	23,000	7,571	5,000	3,286
8th	77,000	51,000	34,000	9,625	6,375	4,250
9th	115,000	75,000	50,000	12,778	8,333	5,556
10th	160,000	105,000	71,000	16,000	10,500	7,100
11th	235,000	155,000	105,000	21,363	14,090	9,545
12th	330,000	220,000	145,000	27,500	18,333	12,083
13th	475,000	315,000	210,000	36,538	24,231	16,154
14th	665,000	445,000	295,000	47,500	31,786	21,071
15th	955,000	635,000	425,000	63,667	42,333	28,333
16th	1,350,000	890,000	600,000	84,375	55,625	37,500
17th	1,900,000	1,300,000	850,000	111,764	76,471	50,000
18th	2,700,000	1,800,000	1,200,000	150,000	100,000	66,667
19th	3,850,000	2,550,000	1,700,000	202,631	134,211	89,474
20th	5,350,000	3,600,000	2,400,000	267,500	180,000	120,000

Find your character level in the first column, and read across to one of the last three columns (according to the campaign's level progression rate) to determine the Relative XP per Character Level.  Ex. a 13th-level character using slow progression has 475,000 XP, which is approximately 36,538 XP per level.

Multiply this result by the hit dice you have earned in each of your classes. Ex. A Fighter 10 / Rogue 3 has 365,380 XP in fighter and 109,614 XP in rogue.  The total XP of all classes should be roughly equal to the XP needed to earn the current level.

Compare each class’s individual total to the appropriate column of the Experience Point Table (according to the campaign's level progression rate). This will tell you your class ability level for that class. Ex. A Fighter 10 / Rogue 3 has class ability levels of Fighter 12 and Rogue 8!

Level Averaging Method

A simpler way of determining Class Ability Level is the level averaging method.  It is not as preciese, but the values are about the same.  Simply use the following formula for each of your [non-prestige] classes, rounding results down:

Class Ability Level = (Class Hit Dice + Character Level) / 2

If Character Level is 10 or lower, lower the Class Ability Level of each class by 1 (minimum equal to Class Hit Dice).

This method works well in campaigns that are not using experience points.

Class Ability Level vs. Class Hit Dice

Determining which abilites "Scale" with Class Ability Level and which scale with Class Hit Dice will be a matter of trial and error for a while.  In general, class abilities that improve as "class level" increases generally improve when Class Ability Level increases--unless they are explicitly tied to Class Hit Dice.

Class abilities that are affect or are affected by systems outside of the microcosm of the class itself are tied to Class Hit Dice.  Examples include:

• Caster Level remains bound to class hit dice (and prestige class bonus), not class ability level. While a multi-class spellcaster casts spells according to his/her class ability level, those spells are bound to the lower caster level when applicable.  Caster level can also be increased by some prestige classes; the manner of these increases is explained in the class ability description.
• Animal Companions, Eidolons, Familiars, etc. gain power (or may be improved) as Class Hit Dice increases--though these companions may still interact with other abilities of the class (such as higher level spells that can be cast through them).
• Bonus Feats are gained in relation to Class Hit Dice.

Prestige Classes are the exception to this modified system. One class hit die in a prestige class is always the same as one class ability level in that class.

Edited October 14th, 2015.