This series follows the trials, tribulations, successes, and failures of a fairly inexperienced GM who has recently picked up the hobby after a long time away. It aims to assist new GM’s by examining what worked, didn’t work, and what failed miserably as he spins up new campaigns, modules, encounters, and adventures for his friends and family in Fantasy Flight Games’ Edge of the Empire/Age of Rebellion/Force and Destiny system.
This is the final part in my series devoted to mass combat used in your own roleplaying games. I am using, as a basis for the discussion, the rules for mass combat in the Star Wars RPG lines from Fantasy Flight Games. In Part 1 I introduced the system included in FFG’s game lines overall, and explained how I structured my first mass combat adventure for my players. In Part 2, I reviewed the changes I made after our first session, and the things I did to improve the adventure going forward. I talked a lot about the connectivity and synergy between all the phases and making the actions the PC’s do in their encounters affect the overall phases of battle.
Much of the discussion centered around the system developed by FFG for the Star Wars game lines. But after building mass combat adventures in the system, and working through its mechanics, I believe a similar system can be implemented in just about any d20 system. So what you’re about to read is quite experimental and a bit of a reach. I’ll be anxious to hear responses and ideas from readers on the subject.
At its heart, the mass combat rules of FFG’s system center around the concept of phases of battle, and a roll between each phase to determine the ebb and flow of the battle around the characters. While FFG does this using their trademark narrative dice, I think we can accomplish the same thing in d20, with a bit of tweaking. Here is an example of how to possibly port the mass combat system into a d20 game.
First, we need to decide how difficult the battle is. This determines what number on a 20-sided die the PC’s need to roll to “win” each phase. This is similar to estimating the attacking and defending forces in the FFG system. For our example, imagine a Dungeons & Dragons type d20 game where the party has to assist a king’s army in besieging a large castle. Our PC party will be part of the attacking forces. The king has several companies of forces including soldiers and archers, as well as a line of catapults behind the walls. The gate is heavy and reinforced with no side or back entrances. The attacking forces have a battering ram, heavy horsemen, soldiers, and archers. The attackers are led by an experienced captain, a ranger with over 20 years of battle experience. The defenders are led by a king who has defended his castle on several occasions.
Let’s say on paper, the battle is a 50/50 shot to start. So, the PC’s need to roll an 11 or higher on a 20 sided die on their mass combat check between the phases. This can be modified, however, based on what we know about the attacking or defending forces. The higher the number needed on a d20, the harder it is for the PC’s side to win. Perhaps the defenders are tough and behind a huge, reinforced wall. Let’s add +2 to the roll (now 13 or higher). However, the attackers have a battering ram, so let’s subtract -1 (for a roll now needing a 12 or higher). The defenders are led by a king who is used to defending this castle, so we’ll add +2 to the roll. But the attackers have a better commander than the defenders’ king, so we’ll subtract -3 from the roll. Finally, the defender’s catapults add an element the attackers cannot duplicate, adding a +2 to the roll. So our base mass combat check roll needed by the PCs between the phases is a 13 or higher to ‘win’ the phases.
Second, we need to split our adventure into phases. We could split things up like this:
Phase 1: The attacking army arrives at the castle. A battering ram is deployed and used on the large front gate. Archers from the inside of the castle try and thin out the attacking force while a small group of soldiers attack the battering ram.
Phase 2: The attacking army manages to breach the castle walls somehow. The fight spills into the outer edges of the interior of the castle.
Phase 3: The defenders have to stay vigilant long enough for the attackers to be thinned out. The king retreats to an emergency shelter inside the castle. They must defend the king and ensure he lives while causing the attackers to retreat.
Next, while the PCs play each phase, set up an encounter for them. If they are successful in the encounter, adjust the mass combat roll needed down. If they are defeated, explain narrative reasons why the mass combat roll needed is increased. This part is key because it is how the FFG mass combat system elegantly connects PC actions and consequences to the larger battle. Let’s look at the first phase for a possibility.
Phase 1 encounter for the PCs: The team must protect a group of attacking NPCs using the battering ram to break down the front gate. The defenders send a squad of soldiers out to destroy the battering ram. The PCs must defend the battering ram while it tries to bring down the castle’s front gate.
If the PCs defend the battering ram and the NPCs using it for 5 rounds: Subtract -2 from the mass combat roll leading to phase 2, the attackers can breach the gate soon.
If the PCs allow three or more NPCs using the battering ram to die in 5 rounds: Add +2 to the mass combat check before phase 2, the ram is nearly destroyed.
So now the fun part…the mass combat check! Not only that, we need to determine what happens depending on the roll. The GM should have this pre-planned and should be ready for both winning and losing the check for the PC’s. Not only have narrative ready, but the mechanical effect on the mass combat roll. Things like:
If the PCs win the check: The battering ram is safe. After several minutes of smashing it into the castle gates, the gate falls in allowing attacking troops and heavy cavalry to pour into the front of the castle. The army surprises the defenders and is able to destroy several of the catapults behind the walls, ensuring that many more troops survive. Between phases 2 and 3, the mass combat roll gets a -2, making it easier for the PCs to win the next check.
If the PCs fail the check: The defenders kill several of the men assigned to the battering ram. The gate holds much longer, and as a result, many more attackers perish trying to scale the walls. Half of the heavy cavalry is wiped out from the catapults which are still in operation. All attackers must use ladders to scale the castle walls at great cost. Between phases 2 and 3, add a +2 to the roll needed to win, making it harder for the PCs.
Keep putting encounters together for each subsequent phase that involve the PCs. Make each success or failure affect the difficulty of the mass combat checks. Just keep track of the magic number the PCs need to roll at least to win each phase of combat. Adjust it up and down depending on what the PCs accomplish or fail, as well as the result of the previous mass combat check. Keep carrying the number needed from phase to phase as it adjusts. If you do this, you should be able to connect the phases and PC encounters, all escalating to a climactic finish. If the PCs win the final check, the larger, overall battle is a success for the PCs as well. Or, if they fail the last check, perhaps regardless of how well the PCs fought, the army was simply unable to kill the king and take the castle. Now we have an uncertain, dynamic backdrop to the PCs exciting encounters and can make them feel responsible in part for its success or failure.
This idea is quite an experiment so please tell me what you think! Can you adopt this phased mass combat mechanic into a d20 system? How well would this work? Would you adjust it in any way? I’m truly interested in responses because my players felt that mass combat was a great type of adventure that really made things feel epic and cinematic for the group.
Thanks to all for allowing me to take a deep dive into the construction of mass combat encounters! I hope you enjoyed the series.
Scott Alden
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