Facing

Facing describes a player or NPC's orientation in relationship to another unit, or simply a given direction. It is almost always phrased as a binary condition - a character is either facing the specified unit or direction, or it's "facing away", with 90° to either side of the unit's exact front acting as the cutoff. Being front-facing is another way to say the unit is facing what was specified. Facing is variously used to determine whether one unit can attack another, the effectiveness of spells or abilities, and the applicability of defensive statistics.

The exact front of a player is the direction the player will go if they press their forward movement key (and no others). NPCs will almost always face exactly in the direction of their current target, especially when they are attacking it. Unit models are also crafted so that the eyes and head aim in the direction of the exact front of the unit most of the time, although occasionally this can be deceptive. Any two units that are less than half a yard apart, measured from center to center, are always considered to be facing each other.^{[citation needed]} 

NPC facing can typically change in any direction instantly, while player turning is limited by the speed of the mouse (or the key turn rate). Some channeled spells will automatically and instantly turn a player to exactly face the target, and may continue doing so as long as casting continues. [Shadowstep] and other short-range teleport abilities may change the player's facing; these abilities also change a target's facing towards them due to the fact that they are now in a different spot. Teleports are essentially the only way to get behind a mob that is targeting the caster without incapacitating it somehow - the slight delay before it instantly turns to face the player's new location may be enough to take an action, though reflexes must be quick and lag must be low.

Players can only dodge, parry, or block attacks when front-facing the attacker, while Mobs can dodge but not parry or block attacks from behind. Therefore, attackers should always prefer attacking from behind, but this is particularly true of melee characters, who are vulnerable to parrying and can more quickly maneuver to different sides of a target. This also means that melee attackers selecting gear at high levels will want to focus on mitigating bosses' dodge chances with expertise, on the assumption they'll be able to attack from behind.

Most attacks and offensive spells require that the target be in front of the attacker to start and finish the attack or spell. If a player is not front-facing a target for an ability requiring it, "Target needs to be in front of you" will be displayed as a warning, and the attack or spell will not initiate. After initiating casting, characters may turn away from the target momentarily and turn back without ruining such a spell cast. Many debuffs and damage over time spells don't check facing, and may be used while looking or even running away from the target. This more often applies to instant cast spells than those with a cast time. Nearly all spells targeted at friendly units, particularly healing spells, also do not require any facing, nor do most ground-targeted area of effect spells, which can target an area behind the caster's back.

Some abilities not only check the caster's orientation but also require a certain facing from the target. For instance, [Backstab] and [Ambush] can only be used from behind. Slightly less restrictive are abilities that have a greater effect from behind, such as [Paralysis]. On the flip side are the attacks that have full impact when the target is facing the user, usually involving an attack of some kind on the eyes: [Gouge] can only target someone facing the user, and some boss abilties like Eadric the Pure's Radiance require players to turn away.