Here are some quick rules I created for 2e style multiclassing:
You can have one, two, or three classes.
XP maximum is still kept the same (355, 000) which is divided between your classes. This means that with 2 classes, you can reach levels 15/15; with three classes you can reach levels 12/12/12.
Hit dice are combined together and divided by the number of classes and rounded down.
A fighter/mage/rogue would have d10+d6+d8 for a total of 24/3 or d8. A fighter cleric would have (10+8)/2 or 9 rounding down to d8.
If you would gain an ability score increase in each of your classes at the same level, you instead gain it only once.
Proficiency bonus* is based on your current level. This means a triple class would top out at +4, dual class at +5 whereas a single class reaches +6.
Spell slots follow the most beneficial progression (An eldritch knight/paladin/wizard has spell slots as a wizard).
Pros
- You gain a lot of abilities from each of your classes.
- You have the best spell slots out of all of your classes.
Cons
- You have a lower maximum level which means:
- Lower proficiency bonus.
- Lower overall hit points.
- Less ASIs (both dual and triple classes miss out on the level 16 and level 19 ASIs, mitigated somewhat with fighter or rogue)
- You level slower than a single classed PC, this might impact survivability.
*If I ever end up using this, I'm thinking about making the proficiency bonus scale with XP equivalent instead of character level so that a 12th level fighter/mage/rogue still ends up with a +6 proficiency bonus.