Old-school Multiclassing in 5E: rule variant
Remarks on game balance: with this variation, you gain some potential synergies that in some ways make a fighter/mage more powerful than a fighter and a mage working together. For instance, you can wear heavy armor and cast a Blur spell and Shield when hit, which is more than twice as good as either heavy armor or Shield + Blur spells by itself. But despite "costing" as much XP as a fighter and a mage put together, you're more fragile (fewer HP) than a fighter and a mage working together, you do less damage (get half as many attacks), and your attributes are spread thinner because you're only getting half as many ASIs to boost both your spells (Intelligence) and your fighting (Dexterity or Strength). It's an open question whether a party of multi-classed PCs is stronger or weaker in practice than a similar XP total PCs using standard PHB multiclassing, but at least it's less fiddly, and you won't have to worry about 2-level warlock "dips" and sorlocks! ~Max
Rule 0.) For purposes of this discussion and for historical reasons, 5E PHB-style multiclassing will be referred to as "dual-classing" and this proposal will be referred to as "multi-classing". Where ambiguity exists, this proposal may be referred to as "concurrent multiclassing" or "old-school multiclassing" to resolve the ambiguity.
Rule 1.) Dual-classing and multiclassing are mutually exclusive and must be decided at character creation time. You cannot dual-class and multi-class with the same character. Some DMs may wish to impose additional restrictions, e.g. only humans can dual-class and only demihumans can multi-class, or perhaps only certain multiclass combinations are available (e.g. paladin/warlock/rogue may not be an option). Do what works for your campaign.
Rule 2.) When you multi-class, you may have either two or three classes. You split your experience among them evenly and level them up simultaneously.
Example: John is a 1st level fighter/rogue. He earns 300 XP from adventuring, which gives him 150 XP as a fighter and 150 XP as a rogue. Since he needs 300 XP to reach 2nd level and has only 150, he does not level up until he gains another 150 XP in each class.
Rule 3.) You must meet the same ability score prerequisites as a dual-classed character, using the usual PHB table for multi-classing ability score prerequisites.
Rule 4.) At first level, you may take the best HP, armor and weapon proficiencies of all of your classes. You may select one of your classes from which to gain saving throw proficiencies--you do not gain all saving throws from all of your classes.
Example: Rupert is a 10th level Hunter/Battlemaster/Illusionist. Because Battlemasters are proficient in all weapons and armor, Rupert is too. Because Hunters and Battlemasters both have d10 (6), Rupert does too, even though Illusionists have only d6 (4). When he goes up to 11th level, Rupert will gain d10 (6) HP plus his Con bonus. Rupert is proficient in Strength and Constitution saves because he chose at first level to take his saving throws from his Fighter class.
Rule 5.) Class features with the same name may only be gained once. For purposes of this rule, "Nth level ASI" is considered a distinct feature. Spellcasting is an exception (see rule 6).
Example: Rupert is a 10th level Hunter/Battlemaster/Illusionist. He has one fighting style (Archery) chosen as a fighter at first level; he has earned 3 ASIs so far at levels 4, 6 (as a fighter), and 8.
Rule 6.) Spellcasting is tracked separately for each class. You cannot mix and match spell slots or spell points between classes unless they are the same type of spellcasting, i.e. come from the same class spell list. (So basically, Arcane Tricksters and Eldritch Knights are cumulative with wizards.)
Example: As a 10th level Hunter/Battlemaster/Illusionist, Rupert has 4/3/2 slots for Ranger spells (or 27 spell points by DMG spell point rules) and 4/3/3/3/2 slots for wizard spells (or 64 spell points). Wizard spell points/slots cannot be spent on ranger spells, and vice versa.
Example: Rupert's friend Durk Dursley is a 10th level Eldritch Knight/Abjuror. Durk has 4/2 wizard spell slots (17 spell points) as an Eldritch Knight and 4/3/3/3/2 wizard slots (64 spell points) as an Abjuror, which means he has a total of 6/5/3/3/2 (81 spell points) wizard spell slots (spell points) to spend on any wizard spells he knows as an Eldritch Knight or has prepared as an Abjuror.
Note: when Rupert's single-classed friend Olaf the Stout is a 17th level wizard with 240,000 XP and 107 spell points with access to 9th level wizard spells, Rupert will still be 10th level with 80,000 XP in each class and 91 total spell points with access to 3rd level ranger spells and 5th level wizard spells.
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If I esteem mankind to be in error, shall I bear them down? No. I will lift them up, and in their own way too, if I cannot persuade them my way is better; and I will not seek to compel any man to believe as I do, only by the force of reasoning, for truth will cut its own way.
"Thou shalt love thy wife with all thy heart, and shalt cleave unto her and none else."
