Cover and Flanking

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 light cover and a tree trunk that gives heavy cover, the target has heavy.

A target with light cover has a +2 bonus to AC and Dexterity saving throws. A target has half cover if an obstacle blocks at least half of its body. The obstacle might be a low wall, a large piece of furniture, a narrow tree trunk, or a creature, whether that creature is an enemy or a friend.

A target with heavy cover has a +5 bonus to AC and Dexterity saving throws. A target has three-quarters cover if about three-quarters of it is covered by an obstacle. The obstacle might be a portcullis, an arrow slit, or a thick tree trunk.

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. A target has total cover if it is completely concealed by an obstacle.

Flanking

When you and an ally are flanking a foe, it has a harder time defending against you. Creatures that are successfully flanking gain +2 to hit the creature they have flanked.

To flank a foe, you and your ally must be on opposite sides of the creature. A line drawn between the center of your space and the center of your ally's space must pass through opposite sides or opposite corners of the foe's space. Additionally, both you and the ally have to be able to act, you must be wielding melee weapons or be able to make an unarmed attack, you can't be under any effects that prevent you from attacking, and you must both have the enemy within reach. If you are wielding a reach weapon, you use your reach with that weapon for this purpose.