helsmuth

Open Mass Combat System Mongoose Publishing introduced the OMCS in Seas of Blood (2001), then expanded upon it in Quintessential Fighter (2002). Of all the mass combat systems I've come across for D20, this one is the easiest to convert a creature stat block into its corresponding mass combat statistics. Unit Hit Points (UHP) are equal to the total number of hit dice for all members of a unit, adjusted by Constitution modifier (and possibly by Toughness feat). Cavalry units receive a 50% bonus to account for their mounts. Particularly large or small units receive a modifier to damage from their ranged attacks. And then you're basically done. You roll a single to-hit roll for the entire unit, which is just the ordinary to-hit modifier for a single member of the unit, adjusted by the relative size of the unit and its target (eg. if a unit attacks another unit half its size, it receives +1 to hit and a x2 damage multiplier. Conversely, it's opponent is at -1 to hit). You...