Clearer interpretation: case 1.
A major difference: case 2 uses a different Y than case 1. But that's assuming you're using some wacky system that makes it practical to attack
non-stop.
A different system might require you to expend effort defending, as well as attacking.
As an aside (to an aside), I suspect math isn't the issue for most people. The simulationists want to imagine blood, the (video) gamists want to shrug off damage. Why can't they imagine whatever they want?
In case I haven't derailed the thread already, isn't DoaM just a way to oppress the wizard-characters? Let's get some wizard-love, people!
Interesting. I myself find the second case clearer, with an interpretation of "the attack is so tenacious and threatening that a major effort is required to avoid a serious blow." Then, the major effort required means that damage is applied even on a miss.
That is, I'm thinking of the the DOAM amount as representing a baseline / minimal effort required when engaged by the attacker, and the DOAH amount represents extra damage when the attacker was able to push past defenses and (depending on the interpretation of a hit) score a blow / cause extra effort / use up some of the defender's luck.
I do see that having just one damage amount applied (either the DOAM X or the DOAH Y amount) is much simpler than having
either one or two damage amounts (either the DOAM X amount or both the DOAM X amount and the DOAH Y - X amount), and is simpler because a DOAH Y - X amount will be constrained to what is easy to calculate.
But, even though I prefer the case 2 interpretation, I get into a tangle with it, because, if fighters can have
Implacable attacks, I wonder whether there should be other attackers that have this ability. But, if only fighters can get the ability, this seems to be truly an exception case, and I find these to be distasteful when they don't have a good reasoning behind their existence.
Looking at several existing 3E continuous damage cases: Being on fire; standing next to a wall of fire, the reasoning is different than for DOAM. Also, the actual existing case of DOAM, that is, an attack with a grenade-like weapon, which applies splash damage on a near miss, has a different reasoning. DOAM seems to be truly a new case.
Comparing this with sneak attack dice and with critical hits (both using 3E as a background), I don't find that I have the same problem with these mechanics. You could replace sneak attack dice with an increased critical hit chance, but that doesn't seem to work mechanically as well as sneak attack. The conditions for when to apply sneak attack dice fit the flavor very well. Perhaps critical hits should have been based on the amount the attack exceeds AC, but that moves the excitement from the player to the DM, and adds fiddly details which would slow down combat. Critical hits do have scaling problems -- caused, I think, by poorly thought out feats -- but still, critical hits work pretty well.
Thx!
TomB