Last time I covered how I'd cobbled together a magic system, which has been one of the two major mechanical issues I've had after deciding to "roll my own". The other is combat, which I've decided to essentially wing, starting with something as simple as I can make it and adding stuff from there with the idea of coming up with something functional without being totally arcane.
Base actions have been pretty easy. An attack roll is Strength or Agility + Weapon skill. It is then compared to a target's defense. Defense = Agility roll, unless the target is using an action to Dodge or Parry in which case it becomes either Agility + Athletics/Dodge or Agility + Weapon respectively.
I've also decided that everybody gets two actions per combat round. Available actions are:
Attack, Dodge, Parry, Move, Cast, Grab/Put Away Item
Double dodging is "total defense" and provides a bonus to the roll. Double attack is either "precise" for a single attack with a bonus to the roll or a "all-out attack" with multiple attacks at a minus. Initiative is Alertness + Agility and everybody has to declare actions before they roll.
Damage is a little more, well, fiddly. There are two components, first, the damage die for the weapon, which is taken from D&D. Second, there is how that damage is applied, which is determined by how much greater the attack roll was than the defense roll. This is how I've been doing it:
Attack roll greater by 1-4: Damage is taken off Stun Points (Agility + Vitality)
Attack roll greater by 5-8: Damage is taken off Wound Points (Willpower + Vitality)
Attack roll greater by 9-12: Damage to Wounds PLUS major blood loss of 1D6 additional Wounds per round until wound is treated; no armor damage reduction applies.
Attack roll greater by 13+: Horrible horrible things happen (and no armor DR applies). The main worry with this is that this becomes an opportunity for the DM to fudge things in favor of the players. So far this hasn't been an issue because only the players have gotten these so far. These have happened three times, with the following results:
Dwarf gets 17 greater than a thief in a backalley brawl while wielding a battleaxe. Player rolls 7 on damage. Location roll (using the Zak S. system) is left arm. I rule that the arm has been severed at the shoulder, blood sprays from the wound and the thief has to make a Vitality + Willpower roll to stay conscious. He fails, falls over and bleeds out over the course of the remaining fight.
Halfling gets 13 more than a fleeing Viking while stabbing him with a rapier. Player rolls 1 on damage, with a Location of right leg. I rule that the halfling has caused a bleed as well as hamstringing the Viking, who now moves at half-speed.
Dwarf gets 14 greater than a hired thug while wielding a battleaxe. Player rolls 8 on damage, location roll is head. I rule that the dwarf has decapitated the thug cleanly, golfing his cranium across the room and causing the remaining thug to drop to his knees, pleading for his life (lest you think that this was being easy on the players, he was outnumbered 4-to-1 at this point).
As noted above, armor is applied as DR using the AC bonus from D&D to the damage roll of the weapon so long as the attack is only 1-8 points greater than the defense roll. I'm thinking that armor will also "take" the damage that it absorbs and will need to be repaired/replaced over time, although I haven't implemented that yet and it will need further thought. The armor check penalty is also applied to any roll involving Agility/Athletics, including Dodging.
I still really haven't worked out how Parry works, especially in terms of Shields. I'm thinking of having Shields be something that can be used to Parry at a decent die-size without having to have an associated skill -- possibly also applying a negative to most weapons when attempting to Parry, with an exception to some, in the case of things like parrying daggers or whips.
Dual-wielding is another issue that I haven't fleshed out either. I think what I'll probably do is allow you to have two attacks to a single attack action with some major minuses to each attack. Attacking while somebody is casting is also still being shaken down, right now if you're hit before you cast, that tacks onto the overall difficulty of the spell being cast.
So far the system has worked out pretty well, the two actions per round make it really clear what you can and can't do and you have to make some interesting tactical considerations -- charging somebody, AKA using a Move and an Attack means sacrificing defense as you no longer have an action to use for a Dodge or a Parry.
One reason in particular that it's been working well is because with such a simple system, it's very easy for me as a DM to tweak and make judgement calls in tricky situations without everybody having to scramble for books and try and see what rules might apply to the situation. It winds up feeling very OSR, combat becomes something of a collaborative exercise in which the DM and the players try and figure out what would make sense out of the chaos of combat, the result of which is that you have a lot more interesting situations than what I'm used to and a more thematically varied combat experience.