Multi-class is obviously not in the game yet, but the more I play BG3, the more I realize a lot of the current game design doesn't work for it, and thought it'd be interesting to point out now. Some thoughts on what needs to change to accommodate this mechanic.
1. Ability Activation Must ChangeThe current activation method of many class abilities via ability buttons - i.e. Sneak Attack, Battlemaster Maneuvers,
will not suffice once multi-classing comes into play.
This is mainly because multi-class characters are allowed to stack multiple special attacks on a single attack. E.G., a Battlemaster/Rogue can apply Sneak Attack AND a Superiority Dice into a
single attack. There will be tons of these combos when the remaining classes are added (Smite, Reckless Attack, Stunning Strike, etc). A unique but important (IMO) scenario that Larian needs to take note too - Paladin/Warlocks will need a way to differentiate which source of magic to fuel their smite. I.e. a Pal 5/Wlk 3 can fuel a level 2 divine smite with either their level 2 pact magic or level 2 paladin slot. There's strategic importance here since Pact Magic slots regenerate on short rests.
The current set-up - select 1 icon pre-attack - won't work (or won't scale well). The only way to maintain the current set-up is to generate multi-class icons (i.e. menancing attack + sneak attack icon), but that won't scale well as you get more abilities or additional classes (think about the # of permutations a 3 barb/3 battlemaster/1 rogue will have.
The easiest solution is probably to follow the logic flow of table top game (add a toggleable prompt for post-hit and reaction). IMO that will fix a lot and also fix reactions not getting abilities applied.
2. In-Game Class InformationThis is something that many people have already asked for, but when multi-classes are added, being able to see a "class table" becomes a necessity.
People are going to want to plan their build and will need to know what abilities can be expected per level. This is extra important in 5e because of how ASIs work in 5e (linked to class level, not character level) and the existence of non-stacking abilities like Extra Attack (i.e. normally a 5 fighter/5 barbarian is a poor idea).
I think this one would be easy to fix - following what Kingmaker has done is likely the most basic solution. Ideally seeing full class abilities is something you pull up any-time during the game, not just at the leveling screen.
Kingmaker Example (Full Class Details):
3. UI UpdatesThe biggest challenge that multiclass will bring is how the Spells Known/Preparation UI is currently organized and displayed. Right now, everything is under 1 spell book, separated by action and level.
Multi-Class Slot Casters (i.e. Wizard/Cleric): The current UI is 90% okay- 5e multi-class casters use 1 set of slots. The issues will be spell preparation - the UI must differentiate which class preparation slot you're using (i.e. Wizard vs. Cleric). The simplest fix will be have separate blocks for each of your classes (Wiz level 1, Cleric level 1), but I can see this becoming very
clunky as you progress in levels. Color-coding might work if Larian wants to keep a "shared" Spell-level block, but you'll still have issues preparing spells that belong in both classes (i.e. Dispel Magic)
Multi-Class Pact/Slot Casters (i.e. Wizard/Warlock):For these combos, the Spell-Prep UI needs to be changed. Warlock spells are auto-prepared, but you might still want to prep the same spell as a wizard for more casts. I don't think it's possible to keep Pact and Slot spells under the same "Level X" tab - it'll simply cause too much confusion.
Displaying Multiple Spell Attack/DC values for Multiple Casting Stats. Minor fix, but the current Character Doll UI will need to be adjusted to show multiple values. Multiclass casters can use different stats for casting (i.e. Wis for Cleric, Int for Wiz), resulting in 2+ stats each.
For this one, I can't think of a good solution outside of having detailed spellbooks for each of your casting class (i.e. like Kingmaker). It does ruin the stream-line character sheet Larian's going for, but I think the details matter as it affects very real game mechanics.
Kingmaker Example (Sorc/Cleric):
Let me know if you think more needs to be adjusted. Or if you know of elegant solutions from different games that can help Larian accomplish this?