Based off an extended Discord conversation, I thought I would follow up here, asking members of the wall to post about the various ways that they run hordes. Many players employ mechanics to weaken or even completely abstract each individual member of a horde to speed up play, and usually also decrease the deadliness of multiple attacks coming against each PC. A fun idea that came out of the conversation, though, was how kinds of enemies are differentiated by the horde rules you use for them. Skeletons may be immune to arrows, go down without an attack roll, one for each damage dealt, but may also inflict 2 HP per adjacent foe without rolling; Kobalds may require an attack, but still go down 1 per damage dealt, and may roll to attack themselves, but rolling as a group, gaining a +1 from each member of the group over 1 to hit and damage, while soldiers of the Golden League may each get their own attack and HP. So, the idea here is to collect many systems to provide resources for GMs to choose to fit their tastes, and the foes they are presenting. I hope we get lots of entries, and you find it useful.
Horde of Hordes
You could give big or mini boss enemies hp over 1hp but keep the bulk to 1hp per enemy or do Mobs adding the number to the roll for attack and effort or something like that. Player attacks kill as many targets as effort done to the attack range.
I think all the options you mentioned are great! I’ve used enemies with 3 Strikes, enemies with 1HP, enemies with 1 HP + DR, and enemies with full hearts. They all work, I think the different mechanics and add some fun and flair to the combat.
I run roll to dodge, and that makes hordes interesting as well. Does a PC need to roll to dodge 10 times for 10 Skeletons? Or do they roll once, with +10 to the Target? I’ve done both, and the “Nice GM” part of me always balks at enemies getting +10 to the TN, but 1, my players can handle it, and 2, they should have a reason to run every now and then.
One idea I’ve been kicking around though, is treating the “Roll to dodge” more like a Save. You can dodge a single attack, you can even dodge 2-4 attackers with a hard roll, but if you get caught in a HORDE?
You’re rolling DEF or dropping to 0 HP, and taking appropriate damage even on a success.
The big idea here is to treat the Save as a movable value. Save vs Damage, Save vs Armor Destruction, Save vs Death. Instead of treating the PCs or the HORDE like a normal “I hit, you hit” exchange, just take a minute to set parameters, define success AND failure, then make the roll. What’s gonna happen if you get caught for a full round in that horde of Kobolds? Probably not nothing.
I’ve only done this twice. Not for two combats, for two rolls. If I remember to bring it to the table in the future, I’ll let you know how it goes!
Zombie Horde: 1 Hit = 1 Kill, 
/, if surrounded roll CON or drop dying
Horde of Rats: /, DEX to kill single rats, they are everywhere, Bite inflicts Basic, could overwhelm a PC
Horde of Bats: /, Hit with effort to deplete, impede LoS or with HARD, Bite inflicts Basic, flys away if hearts are completly gone
My guess is 1 heart is 10 zombies/rats/bats so each damage kills one enemy (like an hp heart), it looks like they give the option for a larger group by adding more hearts so two hearts would be 20 zombies. That’s at least how I’d run it. A two heart zombie horde (20 total zombies) comes at you and you swing your ax with a result of 5 for damage, 5 zombies are slain with the attack but 15 of the shambling mass remains.
it’s meant generic. could be individuals (as zombies) or progress to scare away the bats