Baldur’s Gate 3 – Does Harming a Companion Indirectly with Warding Bond Affect Their Approval in BG3

Raven Dreamer’s answer gives a good overview, but if you’re interested in an exhaustive list of changes, one is available via the independent Baldur’s Gate 3 wiki project. The main article covering changes to basic rules like initiative, healing, resting and more is “D&D 5e rule changes”, and there are also further articles for changes to races, classes, spells and feats. These articles all assume some familiarity with standard 5E rules. These pages are also updated when patches make further changes to the rules used by BG3 (especially ones which fix bugs preventing a rule from operating as it does in the tabletop game).

I would add that there are some changes that are not obvious but have a big impact on the game. As one example, initiative is not a standard Dexterity check, but instead uses a d4 (though the Dexterity modifier is still added). This makes it more likely player characters will end up next to each other in the initiative order, and such characters effectively act simultaneously, able to take their actions and movement in any order they like. Like many of the changes to a basic rule, this has many knock-on effects, such as modifying how many bonuses to initiative work (advantage on initiative rolls is generally changed to a flat bonus of +3 to +5, for example).

A few other significant changes which surprised me and affect power level:

• Ranges for weapons and spells have been reduced across the board (usually to 60ft/18m), and combat generally takes place in smaller areas with a lot of opportunities for vertical movement. Being at least 10ft (3m) above an opponent can grant a bonus on ranged attacks, and likewise being below them imposes a penalty. (By the way, the game can use metric measurements, using rounded approximations of 5 feet = 1.5m, and 1lb = 0.5kg. As an Australian I love this.)
• Cover is not implemented, but objects and creatures can block line of sight.
• Prepared spellcasters can change their list of prepared spells instantly at any time outside of combat.
• Ritual spells don’t take longer to cast, they just don’t use a spell slot unless cast during combat. Some higher level spells are now rituals, including speak with dead.
• As you noted, most spells and effects with a duration longer than 1 minute now just last until the party’s next Long Rest.
• Most potions can be thrown (as an action) in order to make them splash on the ground and apply their effect to multiple characters. This includes healing potions.
• By default the game has a “Karmic Dice” option enabled which prevents streaks of very high or very low rolls. This always acts in favour of the character or creature rolling the dice, and results in shorter more dangerous combat, since everyone is more likely to hit and do higher damage. This gives spells with saving throws a disadvantage vs ones with attack rolls, since the target rolls the dice.
• Humans and half-elves have revised traits to make up for losing their additional Ability Score bonuses (since everyone gets a choice of +2/+1 to any Ability Scores). This includes a “Civil Militia” trait which grants them proficiency in various polearms and shields.
• Spell components (including foci) are generally ignored, so a human wizard can equip a staff and shield and still cast spells. Being silenced (for example by the silence spell) does prevent spellcasting, which along with the vocalisations when characters cast spells suggests an implicit verbal component, but a small number of spells are explicitly called out as being usable while silenced.
• The AC bonus from a shield equipped in the melee weapon set is applied even while using a character’s ranged weapon set.

There are many more, but those give you an idea about the extent of the changes.

• Before you engage, you can separate your characters by either dragging their portraits on the left side out of the row (in which case separation is indicated by the chain breaking), or by right-clicking their portraits and selecting "Ungroup" There should now be more space between the portraits. You can also Toggle Group Mode, i.e. (un)separate all party members, by pressing G.

  

  When they are all separated, they won't move towards each other on their own accord, and you can guide them separately.

  This is also extremely useful for scouting and disarming traps.

• Next thing to make sure of, is to not end the turn of the initiating character until all other party members are actively participating (unless you want other members to join in later, of course).

• For me, it doesn't actually matter whether I engage the enemy in Turn-Based mode or in Real-Time mode (I wonder if it depends on the Difficulty level, as I'm playing on Balanced difficulty, but I wouldn't know why that would matter).

• Once the enemy party is alerted, one or more of them might turn and notice party members that you had hidden behind them. They will still have the Surprised status, allowing for that initial non-challenged round, but if you want them to remain hidden, be aware of this.

• The advantage your party has over enemies is also somewhat dependent on their Initiative, in the sense that once they enter combat they might end up later in the row, with the consequence that they could be attacked (by enemies with a higher Initiative who lost their Surprised status) before they are able to act in the second round.

The steps that always work for me (trying to be as thorough as possible):

• Ungroup (G) and Hide (C for individuals, Shift+C for the entire group) the members of your party you want to engage the unaware enemies with.
• You can switch between Turn-Based and Real-Time modes (of course, in Turn-Based mode it's easier to deal with surprise movements of enemies).
• Place your party members individually, taking heed of the enemies' lines of sight. Remember to make use of higher ground and obstructions for strategic positioning.
• Once you're ready to strike, let the first character perform a visible/ audible action (unless the enemies are currently neutral, it doesn't even need to be offensive, as long as you attract their attention, such as casting a protective spell).
• That acting character will now roll for Initiative, and so will the Surprised enemies.
  Your other characters will remain undetected (unless, again, the changed lines of sight inadvertently caught them and they engage as well).
• You can now freely move your unengaged characters around, in Turn-Based or Real-Time mode. Being caught by Surprise, some enemies' positions might have changed, allowing for or requiring a different approach.
• Once they perform actions (anything that unhides them, really), they will roll for Initiative, and join the fight.