As I continue to try to make combat a little less predictable, and give players (and monsters!) some meaningful choices other than just whether to swing again or run away, I've cobbled together a short list of moves and tactics. My aim here is options that are intuitively grasped and easy to apply in play. All of these maneuvers and tactics may be announced after initiative is rolled, but before any attacks are made for the round. The bonuses and penalties are most meaningful either in low level play, or when used with a system like this one.
Cautious fighting: A combatant accepts a -2 penalty to attack rolls, in exchange for a bonus of 1 to AC against all attacks against it that round. This tactic is especially useful when outnumbered.
Press the attack: The inverse of cautious fighting, gaining a +1 to attack at the expense of 2 points of AC. A party that outnumbers a hard-to-hit opponent might find this advantageous.
Any monster of animal intelligence or greater might choose one of the above tactics.
Beleaguer: Attempting to overwhelm an opponent's defenses with the press of numbers. A beleaguering group makes only one attack, as if it were a 1 HD monster, but with a bonus of +1 to hit for each member. If a hit is scored, damage is done equal to a full round of attacks from the strongest member plus one point per member of the beleaguering group. Thus, a group of four goblins with short swords beleaguering a fighter would do 1d6+4 damage, while a group of four ghouls (3 attacks, damage 1d3 each) would do 3d3+4. A maximum of six creatures may beleaguer an opponent of equal size; four may beleaguer an opponent of half their size, and eight against an opponent of double their size or greater. If the beleaguering force misses its attack with a natural 1, it has inadvertently struck one of its own members determined at random, and does damage as above. Note that a group of creatures surrounding an opponent are not automatically beleaguering; they may choose to attack as individuals.
Animals that attack in packs, such as wolves or rats, and weak monsters that like to make up for their individual weakness with numbers, like goblins and kobolds, are likely to attempt a beleaguering attack.
Parry: An attempt to block a single attack, chosen by the defender. This uses one of the defender's attacks; if it has more than one attack per round, it may choose to perform multiple parries or a combination of parries and attacks. The defender rolls a saving throw vs. death ray; success indicates that the attack is blocked. A weapon used to parry can block an attack up to one die size larger than its own base damage (i.e. before bonuses for Strength, magic, and specialization.) Thus, a dagger may parry a short sword but not a long sword; a short sword may parry a long sword but not a great sword, etc. Metal bracers or gauntlets may be treated as a 1d3 weapon, thus able to parry 1d4 attacks such as daggers and clubs. A target shield is treated as a 1d4 weapon for this purpose (i.e. it may be used to parry attacks up to 1d6), a medium shield is treated as a 1d6 weapon and a large shield as a 1d8. Shields parry attacks within their rating at +2 to the saving throw, and may attempt to parry attacks up to twice their rating (against max damage of 12, 16, or 20 points, respectively) with an unadjusted save, though success destroys the shield.
Parrying must be declared before the opponent's attack is rolled. Device-fired missiles (arrows, bolts, or sling stones) may only be parried with a shield.
Parrying is always an option for intelligent, weapon-using creatures. Monsters with natural attacks may sometimes choose to parry. A bear might bat aside a thrust from a fighter's spear, or a dragon could attempt to turn a sword blow with a sweep of its talons.
Each successful parry against a beleaguering attack neutralizes one member of the attacking group for purposes of attack and damage bonuses.
Optional: On a saving throw roll of a natural 20, the opponent is disarmed. On a natural 1, the parrying character drops his weapon.
Dodge: Dodging is an attempt to exploit a relative advantage of quickness and maneuverability to completely evade the attacks of a larger, more cumbersome foe. The defender must have room to dodge (DM's discretion), and may take no other action, offensive or defensive. A saving throw vs. death ray is attempted, and success indicates that the defender has nimbly evaded all attacks from that opponent for that round. On an unsuccessful save, the attacker must still roll to hit against the defender's normal AC. Dodge may only be attempted against opponents at least twice as large as the defender (in terms of mass/weight, not height.) A pixie could dodge the attack of a halfling, a halfling could dodge the attack of a human, and a human could dodge the attacks of an owlbear, for example.
A successful dodge places the defender up to half its combat movement rate away from the attacker in a random direction. On a natural 20 on the saving throw die, the defender may choose the direction. On a natural 1, the choice belongs to the attacker.
Dodging is a common tactic of small, non-aggressive creatures, which will usually flee at the first opportunity, and of groups of smaller creatures harrying a larger one.