Quite interesting. It produces a particular enviroment, with its own implications.
I'm not sure if the cumulative penalties for attacks are for different attackers, or different attacks. If it is the former, as I said, it makes fighting a 12 headed hydra "easier" than fighting 12 goblins, because the 12 headed hydra is a single oponent, and thus their 12 attacks. If it is per attack, it makes some oponents harder to beat than others, depending the number of attacks (a 12 headed hydra being more dangerous than a Titan, for example, because of the number of attacks). It's not a bad issue per se, it just makes a different scale of CR (the Hydra would be higher level than in regular D&D, Monsters with 1 single hard-hit attack like titans would be lower CR than in regular D&D). "Lurker" monsters that surprise PC as a basic routine (like Phase Spiders) are particularly more dangerous that those that do not, even if they are more powerful in theory. Again, that's not strictly a problem, just have different scale for CR. A phase spider in that system would be 4 or 5 CR above a non-surprising foe of equivalent stats.
I don't disagree at all (though personally, I'd make a 12-headed hydra roll one attack, not 12).
However, assuming your game has hp and levels, and those scale in d&d style, I still doubt your solution really works.
My game does have HP and levels, though HP is greatly scaled down (having over 100 HP at high level is pretty rare), and, as I said, I use a HP/THP system.
AC is only *part* of the problem about 15th level characters ignoring 12 lvl 1 archers. But the main problem is HP. Even for *naked* 15th level PC in D&D, where they don't have untouchable AC, they will obliterate 12 archers. In seconds. Their HP are simply too much, and they can do a lot of damage to several oponents at a time (rapid firing archer, cleaving fighter, and fireballing wizard and you kill the 12 archers in a round). If your game has HP/level, and the damage/level scales too, this is very hard to avoid.
Damage just needs to outscale HP. For example, it's pretty easy for a level 1 warrior to deal 1d10+10 damage (and, as an aside, the system assumes that level 4 is "the average settled adult", which deals 1d10+12 pretty easily). So, if we're dealing 1d10+10 per attack against someone who has a lot of HP and THP (34 HP + 63 THP at, say, level 20), then it only takes about 6 attacks to bring them down or kill them. If you've got 20 guys with crossbows, that's pretty much going to happen to most PCs.
If you've got 12, there's a good chance that the PC will win. Though, in my RPG, there's a decent chance it'll end badly, which is
especially true if they surprise you (you lose your THP, and your AC drops pretty dramatically).
What's your average lvl 1 goblin archer damage? What's your average non-surprised Lvl 12 fighter HP? What's your average lvl 20 ancient dragon damage?
Level 1 goblin archer: 1d10+10 damage (15.5 average).
Level 12 non-surprised warrior HP: 22 HP + 39 THP (61 total). (Though, to be fair, I said level 1 fighters would be in danger against numbers or if the guy was surprised.)
Level 20 ancient dragon damage (I assume colossal-sized): 2d12+30 (43 average).
The trick against the dragon? Don't get hit, recover your THP before he overcomes it (one hit will probably break it), get a ton of damage reduction, etc.
The trick with the goblins? Get cover, get a boatload of damage reduction, don't let them get the drop on you, or design your PC to resist swarm tactics (apply THP to surprise attacks, use the Whirling Movement style, grab multiple instances of the Adapted Style feat for being attacked multiple times, etc.).
If you don't do either of those things, then both dragons and low level goblins are dangerous. If you mitigate the danger from one, you probably can't afford the other while contributing much beyond your own survival. There's a certain natural balance from only having so many character points to work with. As always, play what you like
[MENTION=6668292]JamesonCourage[/MENTION]: I get how your system works in general, but if the party engage in combat against the town guards of their own volition (which was, I understand, the case), how do you justify them being "surprised"?
I wouldn't. "Surprised" only applies when they aren't expecting a fight at all. They can become "flat-footed" in combat by being caught off-guard, but all that does is lower their defenses, it does not completely remove their THP. If 12 guys shoot them from cover while they're walking through the woods and they didn't notice them, though, I'd count it as surprised.
If the party attacked the town guard of their own volition, they'd probably fear volley fire the most (multiple attacks to the same AC), but they could definitely win that fight at high levels with some smart tactics. Waiting to throw area attacks when enemies appear, using cover or corners, etc. As always, play what you like
