Hey Rumrunner, some interesting things here are my thoughts, mostly about the difference between toggles and difficulty levels - I mostly veer towards the latter.
I would like to see a game settings page that includes the following options as Enabled/Disabled:
1) Dialog Dice Rolls (skill checks).
Yep though for me I feel this should be tied to a story mode - I don't think its right to be able to divorce regular difficulties from a key part of d&d which is all the non-combat stuff including failing your checks.
2) Barrels of oil, fire wine, nautiloid tanks, etc.
I think they should weigh a lot lot more, and encumbered status should work at your max weight, not 2x your max weight or however it is done. The throw-ability also - I think the strength requirements for throwing should be raised. I have no problems with the barrels "being there", just being able to lug 5 of them around just feels off - most of the barrel-cheese could be fixed by making it incredably tedious to move them from a to b and stack them up such as no rest/return to camp when encumbered.
3) Mobs can create ground/surface effects.
4) Party members can create ground/surface effects.
Surface effects are one of my favorite things about the game - but burning from surfaces can proc with burning on character at the same time, and then with movement. It can result in a lot of damage. I would dial them down so any one elemental type can only proc once on your turn for 1dx, unless you move. I can understand that people want them removed but they just arn't a big deal for me with potions of fire/acid resistance available everywhere.
I would like them to remain in "core-rules" mode and to see an easy difficulty where mobs don't each all have a fire/acid arrow in their pack, which would reduce the number.
5) Mobs can have Advantage/Disadvantage Based on height.
6) Party members can have Advantage/Disadvantage Based on height.
I think this has to be a both or neither thing. You could have an option to tone down the benefits/disadvantages universally, but since certain mobs are coded to seek height advantage then it would be a bit absurd to be able to turn it off for them without recoding ranged AI.
7) Disengage, Jump, Hide, Throw, Shove are actions unless performed by a Rogue.
I can understand this but I think it would have unintended consequences for the game. It would be interesting to play a version like this so yeah, maybe an optional toggle.
A higher difficulty level where you only had x number of rests before something bad happened would be great. I would also like to see gale explode if you don't resurrect him and attack you in desperation/leave if you don't feed him artifacts.
11) Increase the number of short rests from 1 to 3.
Short rests are bugged as is because they don't advance time so you can buff before short rest, including things like 3 round potions and they are all still up after. But yeah, I would like 3 short rests implemented for "core" difficulty then maybe fewer for higher difficulties.
12) Eldritch Knights and Arcane Tricksters can learn spells.
I suspect this goes against the spirit of these two classes but I don't really mind.
13) Only Wizard spells can be learned.
I think this is a bug/oversight, but if it is in the final version it should be disableable/only for easy difficulty. I would add that it would be nice for higher difficulties for only arcane casters to be able to cast arcane scrolls and likewise for divine casters.
This is the only one which is a hard no from me. I super dislike exhaustion mechanics.
15) Cantrips have no surface effects.
As I said above, I like surface effects but understand that it gets a lot of others upset.
16) Mobs have correct stats, AC, and HP per DnD 5e.
I don't care about this and feel that higher HP and fewer misses will in the long run save a lot of gamers keyboards from excessive nerdrage.
17) Limit to maximum 1 spell + 1 cantrip per turn.
Interesting, but maybe if you wanted to really increase the difficulty you could shift all currently bonus-action spells to actions. Basically I am neither hear nor there on this.
18) Interact with empty containers.
I like this one as a toggle because I think the "checking every container" roleplay player should be catered to. So I don't think this should be tied to difficulty, nor changed across the board. What I would like to see is that if you open a container then click on another container the first one closes, rather than now having 2 container windows open.
19) Allow a maximum of 1 offhand attack per round.
disagree, but mostly because without seeing the whole game its difficut to say what this would mean. Maybe no more offhand attacks than actions? i.e. 2 actions and 2 offhand actions would enable 4 attacks but 1 action and 2 offhand would only allow 2, not 3? Just a thought.
20) Pickpocketing has consequences.
I would like to see merchants either pack up and leave (i.e. just disappear) if they lose too much to a thief, or else not restock their inventory because they are now too broke.
21) All mobs will actively search for hidden characters.
100%, regardless of difficulty level. Better AI dealing with stealth please.
22) Allow only potions to heal in combat.
Would tie it to difficulty. Using your bonus action eating food for minimal healing is a crutch to get players through early levels and is almost always a waste of a bonus action imo. I would like to see it remain in "core" difficulty but be limited to out of combat in hard and higher difficulty.
23) Require food as a resource with hunger effects.
A "Survival mode" would be fun, but I wouldn't tie it to difficulty since its more of a tedium-roleplay element. Toggle would be cool. maybe if you reaaaaaly want exaustion it would be a survival mode feature
24) Mobs can use Magic Arrows.
25) Mobs can use potions and scrolls.
26) Mobs can use throwables (potions, vials, etc.)
As above I would tie them having them in inventory to difficulty level.
27) Mobs cast sleep, hold person, and magic missile more.
28) Double the amount of leader/elite mobs in encounters.
29) Enemy archers and spell casters return to cover between attacks.
100%, but as a higher difficulty level.
The next set IMO are not needed because the player can simply not use them even if available. Others have disagreed with my opinion so I present them as additional options here:
a) No food during battle
b) Only allow one swap of equipment per round
c) No throwing food/potions
d) No Dipping
As per above I would tie no food in battle to difficulty.
Equipment swap is very cheeseable: Attack with big two handed sword, swap to sword and shield end turn is pretty funny. Its a crutch but BG1-2 had on the fly weapon swapping - I would leave it as it is for core difficulty and make it an action for higher difficulties: e.g. there's no real reason, give the games turn based nature, why you wouldn't be able to swap your necklace or rings for another in the middle of a battle or pull out another weapon. I would have to have a think about how it would effect balance.
Dipping should stay imo
Ill add some others:
The "camp full of concentrating followers solo cheese bug"
Classes can only use class-related scrolls
Merchant inventory refreshing tied to purchases, rather than resting
No-reroll mode with no permadeath (I don't know how this would be implemented but basically no tpw full game restarts but if you fail a persuasion check you are stuck with it.)
Heart of Fury/Legacy of Bhaal Mode
Harder difficulties where:
You do not start with revivify scrolls.
Potions are much more expensive.
Enemies are buffed as per your 27-29
Enemy spellcasters who are already buffed with day-long or concentration buffs
Far fewer scrolls on enemies and with merchants
Merchant full inventory and gold is not pick-pocketable
Maybe reduced XP for kills.