Attacks of Opportunity

Beware, moving through enemy squares may provoke an Attack of Opportunity. If you try to pass within 5 feet of an enemy without engaging it, it can use its Reaction to attempt to strike you. This can work to your advantage – if an enemy tries to move past you without engaging (say, to get at someone else) you can use your Reaction to attempt to strike it. This can happen even if it’s not your turn and does not take up your Standard Action.

Cover

Walls, trees, creatures, and other obstacles can provide cover during combat, making a target more difficult to harm. A target can benefit from cover only when an attack or other effect originates on the opposite side of the cover. 

There are three degrees of cover. If a target is behind multiple sources of cover, only the most protective degree of cover applies; the degrees aren’t added together. For example, if a target is behind a creature that gives half cover and a tree trunk that gives three-quarters cover, the target has three-quarters cover. 

The degree of cover is determined by the DM.

Half Cover: A target with half cover has a +2 bonus to AC and Dexterity saving throws.
3/4ths Cover: A target with three-quarters cover has a +5 bonus to AC and Dex saving throws.
Total Cover: A target with total cover can’t be targeted directly by an Attack or a Spell, although some Spells can reach such a target by including it in an Area of Effect.

Item Action

You can take an optional Item Action at any point during your turn, as can NPCs and monsters. This may include, but isn’t limited to: equipping or de-equipping one piece of gear; drinking a potion, flask, vial or other such consumable; applying bandages, healing kits or salves to you or an ally; throwing bombs, caltrops, marbles, oils, grease and so on; using a Scroll, Wand, or other such activated magical item.

Status Conditions

Blinded: A blinded creature can’t see and automatically fails any ability check that requires sight. Attack rolls against the creature have Advantage, and the creature’s Attack rolls have Disadvantage.

Charmed: A charmed creature can’t Attack the charmer or target the charmer with harmful Abilities or magical effects. The charmed creature behaves very favorably towards the charmer and will try to dissuade allies from harming it. The charmer has Advantage on any ability check to interact socially with the creature.

Deafened: A deafened creature can’t hear and automatically fails any ability check that requires hearing.

Frightened: A frightened creature has disadvantage on Ability Checks and Attack rolls while the source of its fear is within line of sight. The creature can’t willingly move closer to the source of its fear.

Grappled: A grappled creature’s Speed becomes 0, and it can’t benefit from any bonus to its speed. The condition ends if the Grappler is Incapacitated or Stunned (see the conditions). The condition also ends if an effect removes the grappled creature from the reach of the Grappler or Grappling effect, such as when a creature is hurled away by the Thunderwave spell.

Incapacitated: An Incapacitated creature can’t take Actions or Reactions.

Paralyzed: A paralyzed creature is Incapacitated (see the condition) and can’t move or speak. The creature automatically fails Strength and Dexterity Saving Throws. Attack rolls against the creature have Advantage. Any Attack that hits the creature is a Critical Hit if the attacker is within 5 feet

Petrified: A petrified creature is transformed, along with any non-magical object it is wearing or carrying, into a solid inanimate substance (usually stone). Its weight increases by a factor of ten, and it ceases aging. The creature is Incapacitated (see the condition), can’t move or speak, and is unaware of its surroundings. Attack rolls against the creature have Advantage. The creature automatically fails Strength and Dexterity Saving Throws.
The creature has Resistance to all damage. The creature is immune to poison and disease, although a poison or disease already in its system is suspended, not neutralized.

Poisoned: A poisoned creature has Disadvantage on Attack rolls and Ability Checks, in addition to whatever effects the poison may have.

Prone: A prone creature’s only Movement option is to crawl, unless it stands up and thereby ends the condition. Standing up uses all the creature’s Movement. The creature has Disadvantage on Attack rolls. An Attack roll against the creature has Advantage if the attacker is within 5 feet of the creature. Otherwise, the Attack roll has Disadvantage.

Stealth: A Stealthed creature is impossible to see without the aid of magic or a Special sense. The creature’s location can be detected by any noise it makes or any tracks it leaves. Attack rolls against the creature have Disadvantage. If the creature successfully attacks from Stealth, the first attack is always a Critical Hit.

Stunned: A Stunned creature is Incapacitated (see the condition), can’t move, and can speak only falteringly. The creature automatically fails Strength and Dexterity Saving Throws. Attack rolls against the creature have Advantage.

Unconscious: An unconscious creature (such as when reaching 0 HP) is Incapacitated (see the condition), can’t move or speak, and is unaware of its surroundings The creature drops whatever it’s holding and falls Prone. The creature automatically fails Strength and Dexterity Saving Throws. Attack rolls against the creature have Advantage. Any Attack that hits the creature is automatically a Critical Hit if the attacker is within 5 feet of the creature.

Exhaustion: Some Special Abilities and environmental hazards, such as starvation and the long-­term effects of freezing or scorching temperatures, can lead to a Special condition called exhaustion. Exhaustion is measured in six levels. An effect can give a creature one or more levels of exhaustion, as specified in the effect’s description. These effects are cumulative.

Level 1: Disadvantage on Ability Checks
Level 2: Speed halved
Level 3: Disadvantage on Attack rolls and Saving Throws
Level 4: Hit point maximum halved
Level 5: Speed reduced to 0
Level 6: Death