d20 Mass Combat System (from AEG Empires)

[Laggy]

This is a brief overview and by no means comprehensive and full, but a good glimpse at the mass combat system I advocate for D&D. Feel free to press me for more details if you're interested.

Creating an Army Unit

A standard army unit consists of 1st level warriors. Their starting stats are either 14, 12, 12, 10, 10, 8 or 12, 12, 12, 10, 10, 10 - your choice.

Hits: Hit Dice are gone, and Hits are in. A Hit is a symbol of just how much damage the unit as a whole can take. The number of hits any single unit has is gotten like so: average out what a creature's hit points would be, then divide that number by five (.5 and higher goes up, below .5 and you go down) to get your Hits. A unit that ends up with less than 1 Hit is not viable for mass combat.
Hits are influenced by unit size.

Initiative: Unchanged from standard d20 rules.

Armor Class: Unchanged from standard d20 rules.
AC is influenced by unit size.

Attacks: Unchanged from standard d20 rules.
Attacks are influenced by unit size.

Damage: Instead of a random number, units do a fixed amount of damage when they hit. The amount of damage a unit does is figured out by adding the minimum amount of damage they can do, plus the maximum amount of damage they can do (add the results of best and worst die roll together essentially, and the damage bonus to both) and then divide that number by 10. Again, round up for .5 and above, and down for below. If an attack ends up doing 0 damage or less, it simply doesn't affect mass combat enough.

Face/Reach: A unit's face is determined by both its own size and its unit size. Reach has negligible effect in mass combat, since the area of affect is too limited. (Reach weapons usually have other properties that come into play, though, such as a lance's increased damage on a charge, or a spear's additional damage against readied charges.)

Abilities: These and their modifiers remain unchanged from standard d20 rules.

Speed: Divide your foot speed by 5 in order to see how many squares you can move in one action. If after applying speed modifiers a unit's speed is reduced to 0, increase it to 1.

Mounted Units: These guys get slightly different rules. First off, a man and his horse are treated as a single creature. In determining Hits, use whichever one has more HP. For speed, use the mount's speed. AC equals the AC of them both divided by two, rounded down by normal D&D conventions. If the mounts can attack, they attack alongside their riders (usually a stomp attack). For the rest, use the higher of the two values.

Unit Size:
In army battles, individual prowess means nothing if you're horribly outnumbered. After all, no matter how good the fighter, sooner or later, superior numbers can wear him down. And so, unit size is almost as important as unit strength. The following are the number involved in unit size scaling (under the assumption that a standard Medium unit is 150 men).

Solo 1-9
Tiny 10-49
Small 50-99
Medium 100-249
Large 250-499
Huge 500-999
Gargantuan 1,000-1,999
Colossal 2,000+

Size Speed Hits Multiplier Attack Modifier
Solo : +4 x1/4 -4
Tiny : +2 x1/2 -2
Small : +1 x1 -1
Medium : +0 x2 0
Large : +0 x4 +1
Huge : -1 x8 +2
Gargantuan : -2 x16 +2
Colossal : -4 x32 +4

Size Face
Solo : 1 square by 1 square*
Tiny : 1 square by 1 square*
Small : 1 square by 1 square
Medium : 1 square by 1 square
Large : 2 squares by 1 square
Huge : 2 squares by 2 squares
Gargantuan : 3 squares by 3 squares
Colossal : 4 squares by 4 squares

Creature Face
Tiny : -2 squares by 2 squares
Small : -1 square by -1 square
Medium : +0 squares by +0 squares
Large : +1 square by +1 square
Huge : +2 squares by +2 squares
Gargantuan : +3 squares by +3 squares
Colossal : +4 squares by +4 squares

*Solo units have a -2 reduction to any creature face bonus they get, reducing it to a minimum of 0. The same applies for Tiny units, but the reduction is only -1.

Also, a larger unit can do bonus damage when attacking a smaller unit. For every 5 over what it needs to hit on its attack roll, a larger unit does +1 damage.

Army Combat: Actions and Phases

Each turn goes in phases. Each phase is always in the same order, and in each phase units move in order of initiative. You can hold an action and act at a lower initiative without changing your initiative; but you cannot hold in such a way as to act before someone with higher initiative next round. Once the round ends, any saved initiative is wasted.

The three rounds are: the Missile/Magic Phase, the Movement Phase, and the Melee Phase. Over these three phases, a unit has two actions that can be spent in any of the three phases. If you spend both actions in an early phase though, then subsequently you will be unable to act at a later time.

A round in mass army combat lasts 1 full minute.

Missile/Magic Phase:

Aim: Spend one action for a +2 competance bonus on your next ranged attack.
Cast a Spell: Whether a single individual in a unit or the entire regiment itself, you call down arcane might to aid you by spending an action. Area of affect has special rules in terms of how much a spell affects an enemy unit: calculate its area of affect or number of targets the spell can hit, compare to the enemy target's unit size and facing (remember that 1 square = 50 ft, or 250 square ft), and have the spell deal a percent of damage as appropriate. Spell damage is calculated the same way regular damage is.
Fire: Spend an action and send lots of sharp things flying through the air at your foe. Range increments still count, so remember that each square is 50 ft. Resolve the attack as a full attack. Use standard d20 modifiers for everything else (-4 penalty for shooting in melee, cover is applicable if at least half of the enemy unit has it... and so forth).
Opportunity Fire/Spells: Designate a target area of unit. If they move into a spot you can fire at on during the movement phase, you can choose to take an action and do so. The action isn't spent until you fire. Only a standard attack is allowed, rather than a full attack.


Movement Phase:

Charge: Spend both actions, gain the usual +2/-2 to attack and AC, then take a move action and get your full attack. You need absolutely clear terrain to do this, and cannot take move through terrain that takes two movement points to cross.
Climb: The unit can climb as per the standard rules.
Forced March: Put your gear away (sheathed swords, stowed shields) and blow both of your actions to move up to four times your speed. Of course, if you get attacked anytime until the next round, you're getting penalties (-2 to AC, along with the above implications).
Man Fortifications: If the square you're in has fortifications, you can use this to become hella tough. Fortifications grant varying degrees of cover, although they require you to remain stationed there.
Recieve Charge: If someone is charging at you, and you are infantry with polearms, you can automatically blow an action to make the bastards pay (and deal that lovely additional damage against charges with polearms). You do not need to ready this action unless you don't know they're there.
Standard Move: Yup, pretty boring.

Melee Phase:

Attack: Standard full attack. If you have iteratives, you can use them, but can't switch targets with them.
Total Defense: Spend both actions, get a +4 dodge bonus.

Feats in Army Combat

Some feats are special in army units!

Cleave: Deals +1 damage on the attacks that it makes.
Great Cleave: Deals +3 damage on attacks; overrides Cleave.
Improved Critical: Also deals +1 damage on the attacks that it makes.
Improved Disarm: Accept a -1 penalty to damage to impose a -2 competance penalty on a unit trying to hit it. Lasts for 1 round.
Improved Trip: Make an opposed Strength check against an enemy unit; the loser gets a -2 penalty to AC against all melee attacks for that round. Usuable once per round.
Mounted Combat: Cavalry units with this gain a +2 dodge bonus to AC.
Point Blank Shot: Aside from norm, the +1 bonus to damage is granted to all ranged attacks (recalculate the damage to determine actual army combat damage, NOT just a flat +1 damage in mass combat), not just ones within 30 ft.
Power Attack: Same as usual, but remember to recalculate final damage, rather than adding it directly.
Ride-By Attack: After a charge, if a cavalry unit still has movement, it can simply keep going.
Shot on the Run: During a standard movement during the movement phase, the unit can make an attack with ranged weapons (only a standard attack, not a full).
Spring Attack: The melee version of Shot on the Run.
Improved Sunder: Impose a -1 penalty to damage to units that attack them (cannot reduce damage below 1). This penalty is permanent for the rest of the battle, but it doesn't stack.
Trample: Move through enemy units without penalty (can pass only one unit per round). Mounts get a free standard attack on the unit.

Weapons in Army Combat
Reach Weapons: Every 5 ft. beyond the base 5 ft. gains a +1 to damage for an army unit that employs them.
Guisarme: Grants free Improved Trip, and makes self immune to the penalty imposed by losing the Strength check.
Longspear/Pike: Grants +2 bonus to hit against a received charge.
Ranseur: Grants free Improved Disarm, and does not suffer the -1 penalty to damage when using it.
Whip: Gains the benefits of both the guisarme and the ranseur.

Sample Unit
150 heavy cavalry (Medium) (1st level Warriors)
Str 12; Dex 12; Con 14; Wis 10; Int 10; Cha 8
Attack w/ lance: +2
Attack w/ longsword: +2
Damage w/ lance: 1 (1d8+1 = 2+9 = 11, 1.1 ~= 1)
Damage w/ lance, charge: 2 (2d8+2 = 4+18 = 22, 2.2 ~= 2)
Damage w/ longsword: 1 (1d8+1 = 2+9 = 11, 1.1 ~= 1)
Hits: 6 (+4.5x1 hit dice, +2x1 con = 6.5, 6.5/5 = 1.3 ~= 1, heavy warhorse = 3, x2 medium = 6)
AC:
10 (+1 dodge, +8 armor/natural, +0 deflection) = 19 (soldier AC)
10 (+1 dodge, +7 armor/natural, +0 deflection, -1 size) = 17 (mount AC)
Final AC = 20, touch 12 (+2 dodge w/ mounted combat)
Saving Throws: For +4; Ref +1; Wil +0
Initiative: +1
Speed: 10 squares (50 ft on mount / 5)
Feats: Mounted Combat, Ride-By Attack
Skills: Handle Animal +3; Ride +5; Spot +2
Equipment:
- Weaponry: Lance; longsword; dagger
- Armor: Banded mail; shield, large wooden
- Mount: Warhorse, heavy and military saddle; studded leather barding