Concealment: Concealment is anything that obscures an opponent's vision, such as tree limbs or smoke, but does not physically block incoming attacks (which would be considered Cover rather than Concealment; see below). The GM must decide whether the defender is about a quarter (-1 to AC), half (-2 to AC), three-quarters (-3 to AC), or nine tenths (-4 to AC) concealed.
Cover: Cover is protection behind something that can actually block incoming attacks, such as a wall or arrow slit. Cover bonuses are as follows:
25% cover: -2 AC 50% cover: -4 AC 75% cover: -7 AC 90% cover: -10 AC
An attack from the unshielded flank denies the target any defensive advantages from a shield. An attack from the rear flank negates the defensive value of the shield and also negates any dexterity bonus.
Invisible opponent: An invisible opponent can only be attacked if the general location is known, and the attack is at -4 to hit. If an opponent is invisible to the attacker, he or she cannot be attacked from behind (or from the flank). Note that more powerful monsters (those with sensitive smell or hearing, or more than six hit dice) will frequently be able to detect invisible opponents; the GM should determine the chance of this according to the creature concerned and the situation. Powerful magical monsters, or those with more than 11 hit dice, will almost always be able to see invisible creatures normally.
Prone Opponent: Attacks against a prone opponent negate the benefit of a shield, negate dexterity bonuses, and are made at +4 to hit.
Rear Attack: An attack from directly behind an opponent negates the benefit of a shield, negates dexterity bonuses, and is made at +2 to hit.
Sleeping Opponent: Sleeping opponents (natural sleep, not magical sleep) may be attacked with the same chance to kill as if the attacker were an assassin. The effect of magical sleep is described under the entry for the //sleep// spell.
Stunned Opponent: A stunned opponent receives no shield or dexterity bonus, and may be attacked at +4.
Two-Weapon Fighting: If a character desires to fight with one weapon in each hand, the off-hand weapon must be either a dagger or a hand axe. The weapon in the primary hand attacks with a -2 modifier, and the off-hand weapon attacks at -4. The character's dexterity bonus (or penalty) for missile weapons is added to both attacks. Thus, a character with a dexterity of 3 would be attacking at -5/-7. However, although penalties can be offset, this rule can never result in a bonus to attacks! The off-hand weapon cannot be used to affect parrying.