Flamestrike
Legend
Okay what about:
- Multiclassed characters are limited to two classes and may not advance past level 10 in each class (i.e. eventually gets to 10/10 at level 20)
- Multiclassed characters gain standard ASIs at character level 4, 8, 12, 16, & 19 instead of by class level (this creates some dead levels but gives someone balancing their levels quicker asi advancement), ASIs at Fighter 6 and Rogue 10 are unaffected
- Classes that gain Extra Attack gain it based on character level instead of class level if both classes are no more than 1 level apart (benefit lost if you level out of the balanced split); Bladesingers also gain their cantrip as an attack ability with this
- Companions (dancing items, primal companions, wildfire spirit, etc.) gain hp based on character level instead of class level
- Monk Four Elements - spell slots can be used to cast Elemental Disciplines as a bonus action (e.g. attack twice then burning hands with a spell slot since you are out of ki) and ki can be used to cast other known spells gained thru spellcasting or pact magic; max ki spent on a spell equals proficiency bonus (ie progresses by character level instead of monk level)
- When leveling up one class, may also make changes to the other class (e.g. a Fighter/Warlock that gains a Fighter level may also swap out a Warlock spell and Invocation), this simulates the split class character as being of one mixed class instead of two classes
Are you trying to make Multiclassing OP compared to single classes, while also making it more complex?