It's that time again. The Evil Man is locked up in his super-fortress surrounded by undead. The Heroes can either Teleport into his base... Or they can aid the army in the final strike against the monstrous horde and the evil citadel.
Provided the later choice is selected,
If your group is anything like mine, that's a big IF. Players love going toe-to-toe with the BBEG and circumventing his minions. In your scenario is there a clear advantage to devoting PC resources to the mass combat vs teleporting to the BBEG?
I need a way to simulate the field of combat - something short of stocking the the table with hordes of individual characters, but more substantial than hand-waving the whole issue of the characters being in war. I think a simple war game could be used to simulate this, but I am really open to ideas.
The scenario you've set up has the PCs an an allied force laying siege to a citadel after dealing with some banners on the defensive. That's the key thing to remember, that the monsters are trying to be as entrenched as possible - creating choke points, holding the line, forcing attackers through deep water, maintaining higher ground, using arrow slits to fire from, etc. If the troop numbers were even then the defenders would have the advantage being fortified.
The PCs' allies are trying to break the siege, and while the PCs might give some commands, the rank and file fighting probably won't involve the PCs very much.
Why? Because they are needed to break entrenched enemy positions. Missions would involve sapping, taking out a ballistae, killing an enemy leader whose forces the PCs' allies can't break past, capturing a spy/noble who knows a secret route into fortress, etc. When I've run these scenarios I prefer to focus on those heroic missions rather than mass combat per se.
However, I do flavor fights to give a sense of a larger conflict occurring around the PCs. For example, here were some things I added to a similar scenario I ran:
* A group of cavaliers - the last survivors of their unit - were fleeing the field of battle and were trying to escape a rout. The bard PC convinced them to fight onward with the PCs' help. I gave the bard PC control of 5 minion cavaliers and then sent the party against an entire military unit (a L+1 homebrew solo that also spawned minions).
* The artificer PC (whose player couldn't make the session) provided Trebuchet support that the PCs could call in with a magical smoke signal. Basically it was a massive damage area encounter power any PC could call upon...with risks.
* Crossing the field of battle to aid a fallen allied commander was a hazard which took healing surges and/or HP from the PCs. This represented artillery fire, random blows, and generally getting knocked around.
Just remembered I also wrote up simple rules for running a battlefield as a skill challenge where successes/failures were determined by certain types of encounters. I could dig that up if you're interested...