Nearly five years later and I am still stuck on this idea. I think about it regularly and still have done nothing with it.
Why do I like this so much? It wouldn't even be especially fun for modern players (probably don't know about Chainmail if they are regular folks recruited to play). I want to make it fun, however.
How can I do that? Let's think what to consider.
1) pre-configured set of minis (or coins, for those of us who don't know anything about minis) in a formation that should be winnable or losable, perhaps barely uneven (player side has move, magical trap / wizard side has an extra unit).
2) the magic of the device causes some of the player-side units to be based on the people (the party) standing nearby. A FM or Cleric will be a Hero, an MU a Wizard.
3) choose / reskin the creatures involved so that they are somewhat familiar, somewhat alien for the campaign. Perhaps this leftover mini-game is from a time when there were still...how old is this ruin, anyway?
4) For 3, note the existing creature types. Bold type simply means I think it would be obvious fun to include this creature type.
Balrog Dragon Elemental
Ent
Giant Hero Lycanthrope
Roc
Super Hero
Troll / Ogre
Wight / Ghoul
Wizard WraithCombat as in the Fantasy Combat table, save that
-a
Wraith (only on the non-PC side of the combat) on an attack roll of 12 causes a Hero or Wizard to change sides (unit disappears and reappears behind non-PC lines at the discretion of the magic)
-a
Hero, after 3 kills, becomes a Super Hero.
-a
Balrog on a roll of 2 destroys part of the playing surface and falls into an abyss, taking all adjacent allies and any adjacent Wizards with it
-a
Dragon can attack distant units with its firey breath but then defends as a Balrog and cannot attack in its next round.
-a
Giant can attack two units at once, but then attacks only as a Super Hero and a Hero.
The PC side should be differently weighted with creatures, perhaps the PC side heavy on humans with only some supernatural allies (see
this post with a note about Swords & Spells for a touch of what I am aiming for, just in flavor, not in complexity).
The Perilous Dreamer Sorry it took me so long to get even this far.