Information Rich Combat Mechanics

June 13, 2017

The Modiphius 2d20 system is one I have used a couple of times to run convention games based around the Conan roleplaying game. I am thinking of adapting it for use in a Megagame.

First, a Quick summary of the 2d20 system:

  • You always roll at least 2d20.
  • You can roll up to three more d20s for situational modifiers, such as other players assisting you, to a cap of 5d20.
  • The roll is compared against an Attribute (usually in the 8-15 range) and a Skill (usually in the 1-5 range), potentially generating 0, 1 or 2 successes for each d20 roll
  • For example if you have an Attribute of 12 and a Skill of 3, and you roll 2d20 and get a 12 and a 2, you have three successes
  • If the number of successes equals the task difficulty, you succeed, and for each extra success you gain a point of Momentum
  • You can then spend Momentum to cool stuff in the game
  • Weapon damage is handled by rolling d6s
  • A damage roll of 1 or 2 inflicts damage equal to the roll, a roll of 3 or 4 does nothing, but rolls of 5 and 6 trigger special effects based on the weapon type (e.g. bypassing armour, or extra damage).

It recently occurred to me that I could adapt this as a mechanic for handling Army/Front level combat in Megagames. Traditional wargame mechanics often involve a lot of counting of various factors, followed by some maths as you try and make sure you reach the golden 3:1 ratio considered the minimum to ensure success in land warfare. In a Megagame there is no time for all this counting, you need to be able to take in the situation at a glance and get on with resolution. At the same time I want rich information from the combat result – if we are only doing a few combats each turn, then they need to actually move stuff around on the map and add to the game narrative.


The situation in Army Group Center’s sector of the Eastern Front on 6 December 1941. This is a German map, the Soviet reinforcements that are about to launch a counteroffensive are not on the map. Sourced from the Dupuy Institute blog.

Generally speaking, formations of Army/Front size are rarely destroyed in combat – the exceptions being encirclement (e.g. destruction of Army Group Center in 1944) and/or running out of space to retreat (e.g. British at the Fall of Singapore in 1942). What is important is how ready is the unit for further combat operations, and what is the momentum on the front.

So I am thinking of a mechanic where we are rolling d10s, and the important factors about a combat formation are readiness, on a 1-10 range, and quality, on a 1-5 range. A rested unit at full strength with brand new equipment would have a readiness of 10 (so most units would be rated nine or less). Quality is something that can be worked out based on historic performance (for World War Two, based on effectiveness scores from post-war quantitative analysis, I would put German units at 5-6, the  UK at 3-5, the USA units at 4-5, and the Russians at 2-3). Units roll a base 2d10, then +1d10 for each supporting unit flanking the enemy. Units then roll 2d6 for damage, but can spend supply points (or play special capability cards) to boost that up to 5d6 (I will have to playtest that cap, or perhaps allow it to be exceeded by special limited use cards).

The force being attacked also rolls for its defence, and the force with more successes is the force that gets Momentum points to spend. Units that are defending get bonus Momentum for defending river lines, urban terrain, mountains and prepared/fortified positions.

So we also rolled some d6 for damage, and while we throw away the 3-4 rolls as in 2d20, in this 2d10 system, the rolls of 1-2 are used for Attrition Effects and the rolls of 5-6 are used for Maneuver Effects.

Attrition Effects

Spend your Momentum points to reduce the targeted unit’s Readiness score by 1-2 points. The defender can also spend Momentum to hold the ground the occupy (the default assumption is that the attack does move the defender backwards) at a cost in Readiness.

In theory with 5d6, if you roll enough 2s you can take a unit from Readiness 10 to Readiness 0 in one attack, in practice its likely to take a while to grind forces down. At a glance in the European Theatre in World War Two, it was pretty hard for any force to sustain continuous operations with land forces for longer than a couple of months (the US/UK tended to run out of supplies first, the USSR to run out of tanks).

Maneuver Effects

This is where it gets more interesting and you can spend Momentum to:

  • reduce your own Readiness losses
  • reduce enemy Political Will (i.e. capture a large number of prisoners, or a city or other vital objective)
  • gain initiative for your side next turn
  • exploit the breakthrough (deep penetration and/or forcing flanking formations to retire)
  • capture enemy supplies that you overrun.

Using the two sets of dice, lets the game create a rich tapestry of potential game information. The downside is getting the players to make those decisions around spending Momentum quickly. This would be the key thing to stress test in playtesting the design.


One way of representing historic doctrine is to programme the first choice a side makes (or perhaps even the first two choices). For example, UK forces could be required to spend their first Momentum effect on reducing their own Readiness losses, Soviet forces on getting a breakthrough, and US forces on maintaining the initiative.


I used to own a copy of a game called Renegade Legion: Prefect, which focused on hover tank battles on a planetary scale. The side that had initiative did nearly all of the movement and combat, while the side without basically sat there and hoped for a counterattack to give them the initiative. That concept bubbled to my head while thinking about this hack.

So my plan for this 2d10 system is that the side which starts the game on the attack holds the initiative. The initiative allows you to attack as many times as you like (up to one per Army formation). The side without the initiative gets a limited number of counterattacks. Both sides can spend Momentum on initiative, with a cumulative penalty for any side holding on to the initiative for consecutive turns. Another way of doing that might be to have an escalating supply cost, so you could hit a point where one side runs out of puff, no matter how well they are doing on the map. Frustrating, but a representation of Clausewitz’s theory of the culminating point.

A zero score for initiative could be taken as both sides are temporarily exhausted and spend a couple of weeks (or longer) resting or maneuvering before one side resumes offensive operations. Maybe both sides would be limited to a small number of attacks, like counterattacks.

Recovering Readiness

Units should recover Readiness quickly. Fifty percent of lost Readiness per two week turn seems okay as a starting position for playtesting. In this system I would just about never remove a unit from play, but at Readiness One I would not allow it to initiate attacks. Front lines would also be continuous – if you run out of actual Army formations, you would just deploy a Readiness One Battlegroup counter.

While Readiness should bounce up and down, quality would change only rarely – perhaps reflecting a unit gaining an elite reputation, or being issued with state of the art equipment in sufficient numbers to have an impact on operations (one Super Pershing does not a +1 Quality increase make).

…and now I really need to get back to revising The Colossus of Atlantis. GENCON is only 63 days away.


Keep it Simple and Awesome

February 28, 2012

I stole the title from an article that was on copyright, but covered success stories for content creators in the digital age – keep it simple and awesome.

So, as much as I like the dice/energy system, it fails the simple test.  Too easy for “The Great Hat Disaster” to bump all the dice, at which point the entire game turn is screwed.  I also could not find enough stuff for the Agents to do that was awesome – it looked too much like being an unpaid intern.

Revised player roles:

  • Imperial Princes (up to 10 players)
  • Great Houses (x3, with 5 players each)
  • Pirates (up to 15 players)

I’m fairly happy with the Senate, no maor changes there.

Combat, because the pirate players are each individuals, I have to drop the idea of Faction based cards for determining victory.

Initially there will be three types of combat units:

  • Raiders (build by Pirates)
  • Cruisers (built by people controlling colonies)
  • Dreadnoughts (built by Imperial players with Atomic Power).

Players are free to trade/gift units to other players (and this is the only way that Pirates can get Dreadnoughts or Imperials can get Raiders, unless they are lucky in combat and capture a unit).  Initially only Imperials control colonies, but as the game progresses, Pirates will capture colonies too.

Later in the game, the Senate will be able to authorise the construction of additional special capability units.  This requires a crisis to trigger, so the players have time to learn the basic combat system before it gets made more complex.

The combat resolution mechanic is:

  1. Draw a card – the card lists a unit type (Raider or Cruiser or Dreadnought)
  2. The side with the most of the unit type wins
  3. The Defender wins ties
  4. The card will list two sets of casualties that the loser takes, winner takes no losses.
  5. Loser retreats.

Casualty results are in the form of [Unit Type] [Loss], where the types of loss are:

  • One unit destroyed
  • One unit captured by enemy
  • All but one unit destroyed
  • All units destroyed.

Initially the Imperial forces have a 2/3 chance of winning battles (because the Pirates probably don’t have Cruisers or Dreadnoughts early on).  The game economy, however, will allow Pirates to rapidly recruit new Raider forces.  This means that the strategic risk of combat is actually borne by Imperial forces – while the chance of losing all your Dreadnoughts is low, losing all of them in an ambush is a great disaster.  This chance of disaster is deliberate, because it will force the Imperials to engage in diplomacy and to work together when there is a crisis.

Pirate players can be bribed by the Empire, gaining the Pirate the designation of Warlord as long as they work for the Empire.

Trade – leaning towards a variant of civilisation trade cards, but simplifying it so each set of trade card lists what the set is exchanged for.  Players get one trade card for each colony world they control.

Civil Wars – ideally I will develop a mechanic that allows the players to resolve the civil war entirely during the period when the GMs are tidying up the map table.  My current idea is to give players “support cards”, which can be traded around.  In the inter-phase, Princes can trigger a Civil War, at which point people spend and compare support cards.

Emperor – to make the Civil War worth fighting, the Emperor will get a lot of beanies to distribute among their supporters.

Maps – looking at having sector capitals that generate atomic power, and colonies that generate trade cards, and some deep space zones for Pirates to skulk in.

Thats where my thinking is at the moment.

Sun & Starship Mechanics (draft)

January 17, 2012


Combat is initiated by an active player at a map table moving their Fleet into a sector containing a Hostile Fleet. The Game Master draws Combat Cards until a card is drawn that grants one player a victory.  The number and type of cards drawn up to and including the final Combat Card determine the casualties both sides take, and any damage to the Sector’s Atomic Power or Capital Dice.

The following Combat Cards exist:

  • Win if greater number of Ships (x2)
  • Win if greater number of Tech (x2)
  • Win if double+ number of Ships (x2)
  • Win if double+ number of Tech (x2)
  • Win if Dynasty Faction (x1)
  • Win if Rebel Faction (x1)
  • Win if House Faction (x5 one for each House)
  • Stalemate: no winner, draw again (x1)

I did consider having Fleet types (Raider, Cruiser, Mauler etc) or Stances (Assault, Siege, Defend etc) but I think that just adds unneeded complexity.

If the two Fleets do not have matching Ship or Tech strength, then 10 of the 16 cards will decide the battle on the first card draw.  If the two Fleets have equal strength in Ships and Tech, then only two of the 16 cards can decide the battle, and either side has a 50/50 chance of winning.  If you outnumber an opponent in both Ships and Tech, you have a 56.25% chance of winning the battle on the first card draw, compared to the opposing Fleet’s 6.25% chance.

I’ll have to make sure in the initial setup that Fleets have different Ship/Tech strength values, to avoid the first few battles being like the Somme.


  • Ship card: lose one or two Ship strength (on two Ship loss a Capital Die is destroyed)
  • Tech card: lose one or two Tech strength (on two Tech loss an Atomic Power is destroyed)
  • Faction Card: winner gains one Ship strength from the loser
  • Stalemate: both Fleets lose one Ship and one Tech strength, Sector loses one Atomic Power and one Capital Die

The maximum number of cards that can be drawn is 15, as once there are only two cards remaining, one of those two cards must be a Faction card for one of the Fleets.

A possibility is that as the game develops, the mix of Faction cards could be changed.  For example, if you slowly add in Rebel faction cards, this dramatically increases the chances of a Rebel victory, even when the Imperial Fleets may outnumber them strengthwise.  For example, if you add four Rebel Faction cards to the deck, then five of the 20 cards result in rebel victory (25% chance).

Another possible twist, is to have the Rebel faction card in Imperial battles indicate that one Ship has deserted to the closest Rebel Fleet.

Trade Mechanics

I am leaning away from using something like Civilization trade cards, mainly because of the maths involved.  What I am contemplating instead, is acquiring a large number of coloured tiddlywink counters, or beads.  A few hundred in half-a-dozen colours should be enough.

Trade counters spawn in Map sectors, where they can be harvested by players.  Once harvested they can be traded.  Towards the end of each game turn, the Operations GM will hold a quick auction.  The player with the most of each trade colour can win one auction.  Other players hoard their tokens for future turns.

The auctions are for beanies, special resource cards useful in Map Operations or other parts of the game.

If a trade colour is banned, then it stops spawning on the Maps.  Auctions will continue for it, so prohibited trade tokens become quite valuable.

Sector Economy

Still changing my mind on this frequently.  Sectors have two key resources Atomic Power (ATOM) and Capital Dice (CD).  CD are six sided, with the number on the die indicating its current value.

A sector can have a maximum of six CD and 20 ATOM.  Minimum is zero.

ATOM cannot move.  CD can be moved between adjacent sectors.  Each move reduces the value of the CD by one.

In the interphase, the Map GM will roll all the CD in each sector, “refreshing” their values (effective players will have spent their capital and reduced their CDs down to value 1).

Any CD that has a ‘1’ value after being rolled is removed from the sector.  Note: if a sector has the six CD maximum, it should lose one CD per interphase.  A bout of bad luck with a burst of ‘1’s indicates a local recession or depression.

The total value of the CD is quickly added together.  if greater than the current ATOM in the sector, the sector gains +1 ATOM.  if there are no CD left, the sector loses -1 ATOM.  Then add some trade tokens.  This will need to be done ten times for each Map.

During the game turn:

  • ATOM can be spent to build CD
  • CD can be spent to build Ship and Tech strength for Fleets

This is designed to be a steady state economy.  Barring external disruption, players should be able to maintain their CD and ATOM in sectors, while replacing damage to their Fleets.  Recovering from collateral damage from Fleet battles is hard.  There will be options elsewhere in the game (Trade beanies, Senate Bills) that can boost sectors back up.

Note: ATOM is what Factions score Victory Points for at the end of the game, so they have a strong incentive to maintain that resource (or to burn that which is held by other players).


This requires two full player actions.  The first is an attack on the sector.  The second action (assuming the attack was successful) can be to either move the CD out, or to spend the CD.

Jump Keys

I am thinking of giving each player a random Jump Key.  Each Key is tied to one specific sector on one of the three game maps.  The Jump Key can be used once per turn to move a Fleet from anywhere in the game to that sector.  Players can buy and sell their Jump Keys.


I am now considering making the resource that Treasury controls be the number of Bills that can be submitted by the other Committees, rather than another version/source of Atomic Power.  A limit of ten Bills per turn, at least one must be allocated for each Committee.  if the Budget fails, then each Committee gets only one Bill as the crisis paralyses the Imperial Government.  I’m hoping to find 2-3 useful functions for each of the five Committees:

  • Treasury Committee: Budget
  • Honours Committee: award Status to players, nominate players to Committees
  • Defence: change Fleet commands, Emperor Mandated Offensives (EMOs)
  • Colonial: grants ATOM to sectors, tax sectors, change Sector commands
  • Security: espionage operations, regulate trade, removes players from Committees.