Post by Peter Watson-Wailes

LemonLord7 and Ripper62 from Reddit compiled these a large set of clarifications to and lesser-known rules. I thought I'd organise the list and tidy up the answers a little. Hopefully you'll find it a useful resource for next time there's an argument over one of them.

Spells

  • Casting a spell as a bonus action means you can only cast cantrips for the rest of your turn
  • But note that it says "bonus action" and not "cast two spells." If have Action Surge then you can use that to cast two fireballs in one turn since no bonus action was used. And if you cast a bonus action spell like healing word and then use action surge, you can still only cast cantrips with both your actions
  • Not all spellcasters can cast spells as rituals
  • Many spells can only target creatures and not objects - check what they can act on
  • Readying a spell requires concentration until the casting or the beginning the next turn, and expends the spell slot whether or not it casts
  • Roll one die only for spells affecting multiple creatures. The rolled damage is applied to every target
  • Charmed targets can't attack the charmer or target them with harmful abilities or spells

Attacks

  • When an Attack of Opportunity happens on someone else's turn, a rogue's Sneak damage can be applied, but a fighter's Extra Attack cannot. The same applies to readied actions.
  • Half cover gives a +2 to both AC & DEX saves. 3/4 cover increases this to +5
  • A round is one turn from every combatant. A turn is when one combatant/group of combatants acts in the round
  • Action Surge does not give a bonus action; it's just poorly worded
  • Attacks of Opportunity happen prior to a trigger, Readied Actions happen afterwards
  • Attacks with nets are always made with disadvantage

Combat

  • If an opponent is within melee range, you suffer disadvantage when making any ranged attack, not just targeting the melee-opponent. This doesn't apply if the enemy is incapacitated
  • All enemy NPCs of the same type have the same initiative
  • You can take your reaction on your turn; e.g., counterspelling Counterspell
  • When something reduces damage, it's resolved before resistance
  • Round different types of damage individually; e.g., if you are hit with Flame Tongue and suffer 9 slashing and 7 fire damage, and you have Resistance to both, you round down each separately

Feats

  • Jack of All Trades works with all ability checks, including initiative rolls and can be used with spells like Counterspell
  • Two-Weapon Fighting doesn't give bonus with reaction attacks
  • It also don't add your ability modifier to the damage of the bonus attack, unless that modifier is negative

Rests

  • You can only have 1 long rest per 24 hours. Taking a second long rest just means you're rested
  • A long rest can be interrupted by up to an hour of activities (combat, casting spells, travelling etc) and still give the benefits it should

Advantage & Disadvantage

  • Causes don't stack - you either have it or your don't
  • Darkness/fog provide cancel out advantage and disadvantage if both targets can't see each other (you can't aim, they can't see it coming)
  • Each gives +/-5 respectively to passive scores, and non-stacking
  • Frightened imposes disadvantage on all attacks and ability checks. The sufferer can't move closer to source of fear, while they have Line of Sight to it

Resources

  • Harvesting poison from a creature is a DC 20 Intelligence (Nature) check
  • Component pouches aren't standard equipment. Buy one if you'll need it

Other

  • If you have Darkvision, treat darkness as dim light (disadvantage on perception checks involving sight and -5 to passive perception)
  • A rolled 1 is only an automatic failure for attack rolls. There are no critical fails or successes on skill checks
  • Taking damage due to falling automatically knocks a faller prone
  • Fall damage caps at 20d6, and stacks by 1d6 for every 10 feet
  • Moving through another creature's space is always treated as difficult terrain
  • Get exactly the character background you want using the Custom Background rules on page 124 of the PHB
  • Unless specified, always round fractions down
  • Perception checks can't be less than a character's Passive Perception