The short answers are Get darkvision!, Turn on the freakin' lights!, or Move away at half speed! because the game makes it very hard to play a
Combat in Darkness
While an overwhelming number of factors can influence the effects of darkness on the characters below, all of those myriad factors can't be covered by this summary. This summary, then, is deliberately the game at its most basic, ignoring everything that can possibly minimize, mitigate, or modify the effects below. I know it doesn't look like it, but it is.
The Situation
For ease of use, consider A and B human level 1 commoners who each took the feat Toughness twice so they can survive a round of combat or two versus house cats, instead of, like, serious specialists in night-fighting or something. Also, A and B are the only combatants and only battling each other--additional combatants on either side make this already difficult-to-quantify engagement impossibly complex.
1. If A and B are in the darkness and neither can see through it...
- Both A and B suffer -2 penalties to their Armor Classes.
- Both A and B lose their Dexterity bonuses (if any) to Armor Classes.
- Both A and B move at half speed.
- Neither A nor B can charge or run.
- Both A and B suffer -4 penalties to Search skill checks and most Strength-based and Dexterity-based skill checks.1
- Both A and B fail if they attempt any checks or activities that rely on sight.
- Both A and B are immune to gaze attacks.
- Both A and B make all attacks with a 50% miss chance due to concealment.
Both A and B, as free actions on their respective turns, make Listen skill checks (DC = the other's Move Silently skill check result). Success indicates general direction to the other.2 Success by 20 higher than the DC pinpoints the other's location.
If either A or B makes attacks without pinpointing the other's location...
- each melee attack is made into a random square within the attacker's reach.
- each ranged attack is made in a random direction at the closest target in that direction.
Either A or B can, as a standard action, make a touch attack with hands or weapons into two adjacent squares.3 Success pinpoints the other's location if the other is in either square. If the other moves to a different location, the new location must be pinpointed.
If either A or B is hit by the other's attack, the defender pinpoints the attacker's location. If the attacker has more than 5 ft. reach or the attack was a ranged attack, the defender knows only the attacker's general direction.
- Neither A nor B can make attacks of opportunity.
- Neither A nor B inflicts precision damage.
- Neither A nor B can use gaze attacks.
Note: Identical rules are used when both combatants are blind.
2. If A and B are in the darkness, and A can see through it, but B can't see through it...
- A gains no bonuses and suffers no penalties.
- B suffers a -2 penalty to his Armor Class.
- B loses his Dexterity bonus (if any) to Armor Class.
- B moves at half speed.
- B can't charge or run.
- B suffers a -4 penalty to Search skill checks and most Strength-based and Dexterity-based skill checks.1
- B fails if he attempts any checks or activities that rely on sight.
- B is immune to gaze attacks.
- B makes all attacks with a 50% miss chance due to concealment.
B, as free action on his turn, makes a Listen skill check (DC = A's Move Silently skill check result). Success indicates A's general direction.2 Success by 20 higher than the DC pinpoints A's location.
If B makes attacks without pinpointing A's location...
- each melee attack is made into a random square within B's reach.
- each ranged attack is made in a random direction at the closest target in that direction.
B can, as a standard action, make a touch attack with hands or weapons into two adjacent squares.3 Success pinpoints A's location if A's in either square. If A moves to a different location, A's location again must be pinpointed.
If B is hit by A's attack, B pinpoints A's location. If A has more than 5 ft. reach or the attack was a ranged attack, B knows only A's general direction.
- B can't make attacks of opportunity.
- B doesn't inflict precision damage.
- B can't make gaze attacks.
Note: Identical rules are used when A can see and B is blind. Also, identical rules are used when A is outside of an area of darkness through which he can see and B is inside an area of darkness through which he can't see.
3. If A is in the darkness and can see through it, and B isn't in the darkness and can't see through It...
- A gains no bonuses and suffers no penalties.
- B can't attack A but, instead, picks a square which he believes A occupies and attacks that square's occupant (if any). Due to concealment, attacks versus the square's occupant (if any) have a 50% miss chance.
- B can't make attacks of opportunity versus A
- B doesn't inflict precision damage versus A.
Note: Because A isn't "blinded by the darkness," A can still make gaze attacks. Because B isn't "blinded by the darkness" B is still vulnerable to gaze attacks. Whether A can use gaze attacks versus B is the DM's call--although technically B should be vulnerable to A's gaze attack (were A to have one), narratively B should probably be immune to A's gaze attack as the darkness in which A resides prevents B from seeing A.
House Rule: Although he's not "blinded by the darkness" the DM may allow a B, as free action on his turn, to make a Listen skill check (DC = A's Move Silently skill check result). Success indicates general direction to the A.2 Success by 20 higher than the DC pinpoints the A's location. My opinion is that there should be no mechanical advantage to blindness--a means to pinpoint an foe's square should be available without having to gouge out one's eyes.
4. If A is in the darkness and can't see through it, and B isn't in the darkness and can't see through it...
- A suffers a -2 penalty to his Armor Class.
- A loses his Dexterity bonus (if any) to Armor Class.
- A moves at half speed.
- A can't run or charge.
- A suffers a -4 penalty to Search skill checks and most Strength-based and Dexterity-based skill checks.1
- A fails if he attempts any checks or activities that rely on sight.
- A is immune to gaze attacks.
- Both A and B make all attacks with a 50% miss chance due to concealment.
A, as free action on his turn, makes a Listen skill checks (DC = B's Move Silently skill check result). Success indicates B's general direction.2 Success by 20 higher than the DC pinpoints B's location.
If A makes attacks without pinpointing B's location...
- each melee attack is made into a random square within A's reach.
- each ranged attack is made in a random direction at the closest target in that direction.
A can, as a standard action, make a touch attack with hands or weapons into two adjacent squares.3 Success pinpoints B's location if B's in either square. If B moves to a different location, B's location again must be pinpointed.
If A is hit by B's attack, A pinpoints B's location. If B has more than 5 ft. reach or the attack was a ranged attack, A knows only B's general direction.
- Neither A nor B can make attacks of opportunity.
- Neither A nor B inflicts precision damage.
- A can't make gaze attacks.
- B can't attack A but, instead, picks a square which he believes A occupies and attacks that square's occupant (if any). Due to concealment, attacks versus the square's occupant (if any) have a 50% miss chance.
House Rule: Although he's not "blinded by the darkness" the DM may allow a B, as free action on his turn, to make a Listen skill check (DC = A's Move Silently skill check result). Success indicates general direction to the A.2 Success by 20 higher than the DC pinpoints the A's location. My opinion is that there should be no mechanical advantage to blindness--a means to pinpoint an foe's square should be available without having to gouge out one's eyes.
- Which checks aren't specified but "includ[es] any with an armor check penalty" (DMG 302).
- The example is "over there somewhere" (DMG 302). This, apparently, still doesn't let one choose to make an attack in that direction; random squares and directions remain random.
- It is unspecified whether this should be separate touch attacks for each square or one touch attack for both squares.
Documentation
All of this compiled straight from the SRD, from the sections on Vision and Light, which references and summarizes but doesn't actually fully detail the condition blind, which, in turn, references and summarizes but doesn't actually fully detail the effects of total concealment. In addition, buried in the Environment section is a treatise on Darkness, which expands on the condition blind and, of course, provides additional rules--specifically, the crazy ones about making random attacks. All of these are taken into account in the cases above.
Check the Treeware!
- The Exploration section on Vision and Light (PH 164-5)
- The Glossary definition of blinded (PH 305) and the Condition Summary definition of blinded (DMG 300)
- The Combat Modifiers section on Concealment (PH 152-3)
- The Environment section on Darkness (DMG 302)