Rules Reminders

A quick page to look up how certain things work in 5E.

General Rules

Ability Check, Attack Roll, and the Saving Throw

• They share the same procedure for determining success or failure. Despite this, the three rolls are separate from each other. If something in the game, like the guidance spell, affects one of them, the other two aren’t affected unless the rules specifically say so.

Vision and Light (PHB 183)

• In lightly obscured area, such as dim light, patchy fog, moderate foliage, disadvantage on Perception checks that rely on sight.
• Heavily obscured area—darkness, opaque fog, dense foliage—blocks vision entirely. A creature effectively suffers from the blinded condition.
• Dim light, also called shadows, usually a boundary between a source of light, such as a torch, and darkness.
• Creature with darkvision can see in dim light as if it were bright light and in darkness as if it were dim light, so areas of darkness are only lightly obscured (see first bullet!) as far as that creature is concerned. However, the creature can't discern color in that darkness, only shades of gray.
• Visibility Outdoors; two miles on a clear day.

Cover when using miniatures (DMG 251)

• Choose a corner of the square the attacker occupies or the point of origin of an area of effect. Then trace imaginary lines from that corner to every corner of any one square the target occupies. If one or two of those lines are blocked by an obstacle (including another creature), the target has half cover. If three or four of those lines are blocked but the attack can still physically reach the target (such as when the target is behind an arrow slit), the target has three-quarters cover.

Damage (PHB 197-198)

• Officially you track your current hit points and not damage taken; this matters when your max hit points changes!
• Damage taken goes through the following game elements in order: (1) any relevant damage immunity, (2) any relevant damage resistance, (3) any temporary hit points, and (4) real hit points.
• Multiple instances of resistance or vulnerability that affect the same damage type count as only one instance.

Delay / Ready (PHB 193)

Delay doesn't exist in 5E and a Ready action doesn't change someone's Initiative.

• First, you decide what perceivable circumstance will trigger your reaction. Then, you choose the action you will take in response to that trigger, or you choose to move up to your speed in response to it. Examples include "If the cultist steps on the trapdoor, I'll pull the lever that opens it," and "If the goblin steps next to me, I move away."
• When the trigger occurs, you can either take your reaction right after the trigger finishes or ignore the trigger. Remember that you can take only one reaction per round.
• The Ready action lets you ready any action you can take, including Attack, but Extra Attack is on your turn (Source).
• When you ready a spell, you cast it as normal but hold its energy, which you release with your reaction when the trigger occurs. To be readied, a spell must have a casting time of 1 action, and holding onto the spell's magic requires concentration. If your concentration is broken, the spell dissipates without taking effect. For example, if you are concentrating on the web spell and ready magic missile, your web spell ends, and if you take damage before you release magic missile with your reaction, your concentration might be broken.
• You have until the start of your next turn to use a readied action.
• If you have an action readied, you can make an opportunity attack, which causes you to stop readying. (Sage Advice)

Free Actions (PHB 190)

Much freer compared to other editions. When not needing special care it includes:

• draw or sheathe a sword
• open or close a door
• withdraw a potion from your backpack [incredibly generous]
• pick up a dropped axe
• hand an item to another character

However, you can only do one of these things, if you want to interact with a second object, you need to use your action.

And note: drinking a potion or administering a potion to another character requires an action. Applying an oil might take longer, as specified in its description. Once used, a potion takes effect immediately, and it is used up. (DMG 139)

Improvised Weapons (PHB 147)

• You don't add your proficiency bonus unless the item resembles a weapon you are proficient with.
• An object that bears no resemblance to a weapon deals 1d4 damage (the DM assigns a damage type appropriate to the object). If a character uses a ranged weapon to make a melee attack, or throws a melee weapon that does not have the thrown property, it also deals 1d4 damage. An improvised thrown weapon has a normal range of 20 feet and a long range of 60 feet.

Initiative (PHB 189)

• The DM can decide the order if the tie is between a monster and a player character. Optionally, the DM can have the tied characters and monsters each roll a d20 to determine the order, highest roll going first.

Innate spellcasting (MM 10)

• If a spellcasting monster needs material components to cast its spells, assume that it has the material components it needs to cast the spells in its stat block. Casting a spell requires all its components unless a trait or feature says otherwise. [So V,S,M where applicable.]

Moving around Other Creatures (PHB 191)

• You can move through a nonhostile creature's space. In contrast, you can move through a hostile creature's space only if the creature is at least two sizes larger or smaller than you. Remember that another creature's space is difficult terrain [doubles movement] for you.
• Whether a creature is a friend or an enemy, you can't willingly end your move in its space.
• If you leave a hostile creature's reach during your move, you provoke an opportunity attack.

Ranged (Spell) Attacks in Close Combat (PHB 195)

• When you make a ranged attack with a weapon, a spell, or some other means, you have disadvantage on the attack roll if you are within 5 feet of a hostile creature [it doesn't mention anything about the creature needing to be armed] who can see you and who isn't incapacitated. This includes spells that use Ranged Spell Attack (but not those few that use Melee Spell Attack).

Ranged Attacks and People in the Way (Sage Advice)

• Target has half cover [+2 AC] if another creature is between you and the target. [Unlike previous editions it doesn't matter where the creature is.]

Sneak Attack (PHB 94)

• The attack must use a finesse or a ranged weapon.
• Needs advantage on the attack roll, or, if another enemy of the target is within 5 feet of it [flanking is not needed!], that enemy isn't incapacitated, and you don't have disadvantage on the attack roll.

Spellcasting

Important general rule: spells do (only) what they say they do.

Also see: House Rules - Spellcasting.

Rituals (PHB 201)

• Caster must also have the spell prepared or on list of spells known, unless the ritual feature specifies otherwise, as the wizard's does.

Bonus Action (PHB 202)

• If you cast a spell with a bonus action, you can cast another spell with your action, but that other spell must be a cantrip.

Components (PHB 203)

• Verbal (V) - Jeremy Crawford: a verbal component must be audible to work. How loud is audible? Up to the DM. [This DM: stated in a clear voice.]
• Somatic (S) - If a spell requires a somatic component, the caster must have free use of at least one hand to perform these gestures.
• Material (M) - A character can use a component pouch or a spellcasting focus [nah on the focus thing, divine casters need components] in place of the components specified for a spell. But if a cost is indicated for a component, a character must have that specific component before he or she can cast the spell. If a spell states that a material component is consumed by the spell, the caster must provide this component for each casting of the spell. A spellcaster must have a hand free to access a spell's material components but it can be the same hand that he or she uses to perform somatic components. [Sage Advice]

Range (PHB 202)

• Once a spell is cast, its effects aren't limited by its range, unless the spell's description says otherwise.

Targets (PHB 204)

• All spells require an unobstructed path from caster to target [but also note that, for instance, Misty Step doesn't have a target but a range of 'Self'].

• If the spell does not say "that you can see" then there is no requirement for the caster to see the target. They still need the unobstructed path.

• In this episode of the Official D&D Podcast, Jeremy Crawford specifically calls out a closed window (at about 34 mins) - and says it blocks casting.

Spell Scrolls (DMG 139)

• If the spell is on your class's spell list you can use an action to read the scroll and cast its spell without providing any material components. Otherwise, the scroll is unintelligible.
• If the spell is on your class's spell list but of a higher level than you can normally cast, you must make an ability check using your spellcasting ability to determine whether you cast it successfully. The DC equals 10 + the spell's level. On a failed check, the spell disappears from the scroll with no other effect. [Scroll Mishap or Wild Surge on a fail is certainly an option.]
• Once the spell is cast, the words on the scroll fade, and the scroll itself crumbles to dust. The level of the spell on the scroll determines the spell's saving throw DC and attack bonus, as well as the scroll's rarity, as shown in the Spell Scroll table.

Classes

Paladin Divine Smite (PHB 82)

• Can a Paladin hit with a Crit and then choose to use Divine Smite and double all his dice? Yep!

Warlock Awakened Mind (PHB 109)

• You sound like yourself when speaking via telepathy, although as DM, I allow attempts at telepathic deception. (Source)