There's a scene in the movie Captain America: The Winter Soldier where something like ten opponents try all at once to grapple Steve Rogers in a tiny space: an elevator. Doesn't go their way.
I want to throw the four PCs in my Pathfinder campaign something unexpected and I'm working out how I would map out a "many opponents in a tight space melee" like this. I thought the archer and the magic user in particular might be put on the hind foot if they and the other two PCs were talking in a ten foot by ten foot room with a dozen melee fighters who suddenly turned on them.
I'm specifically looking for Pathfinder rules on how to deal with the battle map for a fight with more combatants than will fit in the standard grid in a confined space.
I'm at the point where I'm asking "Can I find a way to make this fun for my players?" I'm coming to the conclusion that sixteen humans in a ten-by-ten room is not where Pathfinder excels.
I get that some game systems make some things easier and other things harder. Maybe a grid combat in four squares each five-by-five isn't the best way to do this.
I have the Core Rulebook and I see the lines about Multiple Creatures in a grapple:
Multiple creatures can attempt to grapple one target. The creature that first initiates the grapple is the only one that makes a check, with a +2 bonus for each creature that assists in the grapple (using the Aid Another action).
I'm not looking for feats like Gang up (alternate d20pfsrd.com link). I get why that feat would be handy. My question is more looking for official rules (or third-party rules) to help make that combat fun. Say (for example): "Run a grid but use a 4 by 4 grid, with 2.5 foot squares in place of 5 foot squares. If you do that, be sure to consider A, B, and C..." Or, perhaps, "Throw the grid out the window and instead work from the following four principles...."