|d20 Modern System Reference Document|
This section covers offensive and defensive modifiers provided by position.
Favorable and Unfavorable Conditions
Generally speaking, any situational modifier created by the attacker’s position or tactics applies to the attack roll, while any situational modifier created by the defender’s position, state, or tactics applies to the defender’s Defense. The GM judges what bonuses and penalties apply, using Table: Defense Modifiers and Table: Attack Roll Modifiers as guides.
Cover provides a bonus to Defense. The more cover a character has, the bigger the bonus. In a melee, if a character has cover against an opponent, that opponent probably has cover against the character, too. With ranged weapons, however, it’s easy to have better cover than the opponent.
The GM may impose other penalties or restrictions on attacks depending on the details of the cover.
Degree of Cover
Cover is assessed in subjective measurements of how much protection it offers. The GM determines the value of cover. This measure is not a strict mathematical calculation, because a character gains more value from covering the parts of his or her body that are more likely to be struck. If the bottom half of a character’s body is covered, that only gives one-quarter cover, because most vital areas are still fully exposed. If one side or the other of a character’s body is covered, the character gets one-half cover.
Cover Defense Bonus
Table: Cover gives the Defense bonuses for different degrees of cover. Add the relevant number to the character’s Defense. This cover bonus overlaps (does not stack) with certain other bonuses.
Cover Reflex Save Bonus
Table: Cover gives the Reflex save bonuses for different degrees of cover. Add this bonus to Reflex saves against attacks that affect an area. This bonus only applies to attacks that originate or burst out from a point on the other side of the cover.
Striking the Cover Instead of a Missed Target
If it ever becomes important to know whether the cover was actually struck by an incoming attack that misses the intended target, the GM should determine if the attack roll would have hit the protected target without the cover. If the attack roll falls within a range low enough to miss the target with cover but high enough to strike the target if there had been no cover, the object used for cover was struck. This can be particularly important to know in cases when a character uses another character as cover. In such a case, if the cover is struck and the attack roll exceeds the Defense of the covering character, the covering character takes the damage intended for the target.
If the covering character has a Dexterity bonus to Defense or a dodge bonus, and this bonus keeps the covering character from being hit, then the original target is hit instead. The covering character has dodged out of the way and didn’t provide cover after all. A covering character can choose not to apply his or her Dexterity bonus to Defense and/or his or her dodge bonus, if the character so desires.
Concealment includes all circumstances in which nothing physically blocks a blow or shot, but something interferes with an attacker’s accuracy.
Degree of Concealment
Concealment is subjectively measured as to how well concealed the defender is. Examples of what might qualify as concealment of various degrees are given in Table: Concealment. Concealment always depends on the point of view of the attacker.
Concealment Miss Chance
Concealment gives the subject of a successful attack a chance that the attacker missed because of the concealment. If the attacker hits, the defender must make a miss chance percentile roll to avoid being struck. (Actually, it doesn’t matter who makes the roll or whether it’s rolled before or after the attack roll. When multiple concealment conditions apply to a defender, use the one that would produce the highest miss chance. Do not add the miss chances together.
A helpless foe—one who is bound, sleeping, unconscious, or otherwise at the attacker’s mercy—is an easy target. A character can sometimes approach a target who is unaware of his or her presence, get adjacent to the target, and treat him or her as helpless. If the target is in combat or some other tense situation, and therefore in a state of acute awareness and readiness, or if the target can use his or her Dexterity bonus to Defense, then that target can’t be considered unaware. Further, any reasonable precaution taken by a target, including stationing bodyguards, placing his or her back to a wall, or being able to make Spot checks, also precludes catching that target unaware and helpless.
Regular Attack: A helpless defender has an effective Defense of 5 + his or her size modifier. If a character is attacking with a ranged weapon and is not adjacent to the target, the character can use a full-round action to make the attack, and gain a +5 bonus on the attack roll. If the character is attacking with a melee weapon, or with a ranged weapon from an adjacent square, the character can use a full-round action to deliver a coup de grace.
Coup de Grace: As a full-round action, a character can use a melee weapon to deliver a coup de grace to a helpless foe. A character can also use a ranged weapon, provided the character is adjacent to the target. The character automatically hits and score a critical hit. If the defender survives the damage, he or she still must make a Fortitude save (DC 10 + damage dealt) or die.
Delivering a coup de grace provokes attacks of opportunity from threatening foes because it involves focused concentration and methodical action.
Knockout Blow: As a full-round action, a character can make an unarmed attack or use a melee weapon that deals nonlethal damage to deliver a knockout blow to a helpless foe. A character can also use a melee weapon that deals lethal damage, but the character takes a –4 penalty on any attempt to deal nonlethal damage with the weapon. The target has an effective Defense of 5 + his or her size modifier. If the character hits, he or she automatically scores a critical hit (see Nonlethal Damage).
Delivering a knockout blow provokes attacks of opportunity from threatening foes because it involves focused concentration and methodical action.
A character can’t deliver a knockout blow against a creature that is immune to critical hits.