In hindsight, the penalty probably ought to have been -4 to hit, since this is similar in nature to a called shot (explained below), and I probably should have only added STR to damage once—so 11 HP rather than 14. I'm confident Steerpike will adjudicate on it however he feels appropriate. And I'm quite aware of the normal modifiers for attacking with two weapons, thank you.
Here's the reason I was looking at it as a single attack: Algernon is no more "doing two things" than Baldhart is when she swings her two-handed sword. He is using both hands together, bringing them down in a single action, the heads of the hammers and the knuckles of his fingers flush together—as if he were swinging a single larger hammer. I might have had him take both handles in both hands, for that matter: it would have been a somewhat awkward grip, but his hands are more than large enough to manage it… what penalty would you have considered appropriate for that? Surely not as severe as -4… -2, perhaps? Or -1?
Normally, a round of combat represents more than a single action: there are multiple strikes, blocks, parries, dodges, feints, positioning, etc. going on all at once. It would be pointless to even attempt to model this accurately, so games use abstractions when characters attack. This is just as true when attacking with two weapons as when attacking with one: each hand, and the item in it, is doing more than one thing during those six seconds (in this game). This is why they make the penalties for fighting with two weapons so severe. (Though logically there are three other things I can think of off the top of my head which ought to be changed if they're going to make them that steep—or to have the penalty at all. In all likelihood, I could come up with more, if I bothered putting thought into it. But that's a different discussion.)
In this case, Algernon is not doing that. He's staking everything on a single attempt… which is why the "called shot" penalty seems appropriate: rather than taking what opportunities fortune affords him, he's going for one specific attack, whether the opening is there or not. But this is also why the two-weapon attack penalty does not seem appropriate: he isn't attacking with both weapons in the normal way. (He isn't actually making a called shot to the harpy's wing, by the way: that's just color text. Though given the way he's attacking, the only things he's likely to hit are her head, her shoulder area, or the floor.)
Given the above logic, however, he should only do his STR damage bonus once, since he'd get the same STR bonus when using an actual two-handed weapon in two hands. (Which also doesn't make a whole lot of sense, having the same STR bonus for one- and two-handed weapons. Some versions of D&D do give you an extra HP of damage for using a weapon in two hands. But, again, whatever.)
Even with the milder -2 penalty, he still had a 65% chance of doing zero damage, by the way… a reasonably strong disincentive for doing such things on a regular basis. I wouldn't have tried it at all if I hadn't had the +2 for charging. (Which I still think belongs on damage, but that's the way we're playing it, so I used it.) If he'd had his normal warhammer, it would never have occurred to him—or to me, for that matter—to use his two throwing hammers as a single weapon. (Also, he normally uses a shield, so wouldn't have a hand free anyway.) Unfortunately, no one bothered to pick it up when grabbing everybody else's weapons.
His original intention had been to throw one hammer, then switch the other from off-hand to main hand for melee. He didn't want to take the friendly fire risk in this case… and didn't want to stand there doing nothing, waiting to see if anything else dove at us or either of the harpies got back into the air. Which may turn out to be a poor decision, if it turns out either of those does happen: he won't have a readied attack waiting.
As for "everybody doing it": sure, go for it. As long as you're wielding weapons that can be laid alongside one another and still be equally effective… which pretty much requires blunt mass weapons with square heads which can be placed flush together. In other words, throwing hammers. And nothing much else. In fact, nothing else that I see on the weapons list, or that I can think of which isn't on the list—other than perhaps warhammers. Blades won't work: the angle and surface area of impact are too important for them. Piercing weapons won't work: at best, they'd count as a trident… which is no better than a spear. No other blunt weapon will work, as they all have rounded heads, thus presenting difficulties similar to those for blades, if possibly slightly less severe ones. But, hey, if people would rather be making a 2d4 attack all the time than whatever it is they're doing now—and surrendering whatever it is they normally do with their other hand—that's their business. If STR gets counted twice rather than once, then, yeah, someone with an 18 STR would come out ahead here; someone with a 16 or 17 might consider it a viable possibility.
Assuming, of course, that they'd also rather accept the hit penalty, however great or small it is, than do, oh, say, 2d6+STR, with no penalty to hit, with a greatsword. Given that someone with an 18 STR would, on average, do a whopping 1 HP more with twinned throwing hammers and double STR bonuses than with a greatsword, but would be at a minimum of 10% less likely to hit.…
…I'm thinking there aren't going to be all that many takers on that one.
Here's the reason I was looking at it as a single attack: Algernon is no more "doing two things" than Baldhart is when she swings her two-handed sword. He is using both hands together, bringing them down in a single action, the heads of the hammers and the knuckles of his fingers flush together—as if he were swinging a single larger hammer. I might have had him take both handles in both hands, for that matter: it would have been a somewhat awkward grip, but his hands are more than large enough to manage it… what penalty would you have considered appropriate for that? Surely not as severe as -4… -2, perhaps? Or -1?
Normally, a round of combat represents more than a single action: there are multiple strikes, blocks, parries, dodges, feints, positioning, etc. going on all at once. It would be pointless to even attempt to model this accurately, so games use abstractions when characters attack. This is just as true when attacking with two weapons as when attacking with one: each hand, and the item in it, is doing more than one thing during those six seconds (in this game). This is why they make the penalties for fighting with two weapons so severe. (Though logically there are three other things I can think of off the top of my head which ought to be changed if they're going to make them that steep—or to have the penalty at all. In all likelihood, I could come up with more, if I bothered putting thought into it. But that's a different discussion.)
In this case, Algernon is not doing that. He's staking everything on a single attempt… which is why the "called shot" penalty seems appropriate: rather than taking what opportunities fortune affords him, he's going for one specific attack, whether the opening is there or not. But this is also why the two-weapon attack penalty does not seem appropriate: he isn't attacking with both weapons in the normal way. (He isn't actually making a called shot to the harpy's wing, by the way: that's just color text. Though given the way he's attacking, the only things he's likely to hit are her head, her shoulder area, or the floor.)
Given the above logic, however, he should only do his STR damage bonus once, since he'd get the same STR bonus when using an actual two-handed weapon in two hands. (Which also doesn't make a whole lot of sense, having the same STR bonus for one- and two-handed weapons. Some versions of D&D do give you an extra HP of damage for using a weapon in two hands. But, again, whatever.)
Even with the milder -2 penalty, he still had a 65% chance of doing zero damage, by the way… a reasonably strong disincentive for doing such things on a regular basis. I wouldn't have tried it at all if I hadn't had the +2 for charging. (Which I still think belongs on damage, but that's the way we're playing it, so I used it.) If he'd had his normal warhammer, it would never have occurred to him—or to me, for that matter—to use his two throwing hammers as a single weapon. (Also, he normally uses a shield, so wouldn't have a hand free anyway.) Unfortunately, no one bothered to pick it up when grabbing everybody else's weapons.
His original intention had been to throw one hammer, then switch the other from off-hand to main hand for melee. He didn't want to take the friendly fire risk in this case… and didn't want to stand there doing nothing, waiting to see if anything else dove at us or either of the harpies got back into the air. Which may turn out to be a poor decision, if it turns out either of those does happen: he won't have a readied attack waiting.
As for "everybody doing it": sure, go for it. As long as you're wielding weapons that can be laid alongside one another and still be equally effective… which pretty much requires blunt mass weapons with square heads which can be placed flush together. In other words, throwing hammers. And nothing much else. In fact, nothing else that I see on the weapons list, or that I can think of which isn't on the list—other than perhaps warhammers. Blades won't work: the angle and surface area of impact are too important for them. Piercing weapons won't work: at best, they'd count as a trident… which is no better than a spear. No other blunt weapon will work, as they all have rounded heads, thus presenting difficulties similar to those for blades, if possibly slightly less severe ones. But, hey, if people would rather be making a 2d4 attack all the time than whatever it is they're doing now—and surrendering whatever it is they normally do with their other hand—that's their business. If STR gets counted twice rather than once, then, yeah, someone with an 18 STR would come out ahead here; someone with a 16 or 17 might consider it a viable possibility.
Assuming, of course, that they'd also rather accept the hit penalty, however great or small it is, than do, oh, say, 2d6+STR, with no penalty to hit, with a greatsword. Given that someone with an 18 STR would, on average, do a whopping 1 HP more with twinned throwing hammers and double STR bonuses than with a greatsword, but would be at a minimum of 10% less likely to hit.…
…I'm thinking there aren't going to be all that many takers on that one.
Valar Lord
Mythic Scribe
Grandmaster