D6 To Hit

What do folks think about the viability of using just D6s for OD&D?

Many of the subsystems already rely on the D6 alone. Pretty much just to-hit rolls do not. The advantage of this system for to-hits is that its quick and easy. It uses only D6s. Also, it only includes only the most significant modifiers. This is similar to 4E granting +2 to hit for CA and making it non-stackable. Basically, the smallest D6 modifier is +3 or -3 on a D20, which really boils it down to only the most important factors.

THE BASICS:
Roll 1d6 to hit. Rolling high is good.
BASE AC: 4 (i.e., 50% chance to hit)

ARMOR TYPE:
Target is heavily armored (soldier-type; plate): -1 to hit
Target is moderately armored (average type critter; chain mail): +0 to hit
Target has light or no armor (brute-type; leather): +1 to hit
Advanced option -- Attacker using appropriate weapon (mace vs. heavy armor, for example): +1 to hit
Advanced option -- Attacker using inappropriate weapon (light blade vs. heavy armor, for example): -1 to hit

Note that Plate was typically AC3, Chain around AC5, and Leather AC8; 10-15% jumps. Our 1/6 variation in odds makes heavy armor a bit more valuable than it is in the D20 system.

CIRCUMSTANCES: Select only the largest bonus and penalty that apply.
Attacker has significant advantage (flanking, striking at unprotected rear, surprise, charge, etc): +1 to hit -- one time only (so flanking, surprise, and charging still gives only +1)
Attacker has exceptional advantage (helpless defender): +2 to hit
Defender has significant advantage (cover, concealment): -1 to hit
Defender has exceptional advantage (battlements, arrow slit, etc): -2 to hit

MANEUVERS:
Defender is parrying: -1 to hit
Advanced option -- Defender is parrying with shield: -2 to hit
Attacker is not proficient with weapon: -1 to hit
Advanced option -- Attacker is making an Opportunity Attack: +/- HEART (WISDOM) modifier to hit

RELATIVE LEVEL:
Fighting Man vs. Tier 1 Monster (1-4 HD): +0 to hit
Fighting Man vs. Tier 2 Monster (5-8 HD): -1 to hit
Fighting Man vs. Tier 3 Monster (9-12 HD): -2 to hit
Fighting Man vs. Tier 4 Monster (13+ HD): -3 to hit
Hero vs. Tier 1 Monster: +1 to hit
Hero vs. Tier 2 Monster: +0 to hit
Hero vs. Tier 3 Monster: -1 to hit
Hero vs. Tier 4 Monster: -2 to hit
Superhero vs. Tier 1 Monster: +2 to hit
Superhero vs. Tier 2 Monster: +1 to hit
Superhero vs. Tier 3 Monster: +0 to hit
Superhero vs. Tier 4 Monster: -1 to hit

This looks busy, but really isn't. If you're of appropriate level, you get no modifier. If you're higher level than the monster, you get a bonus to hit. If you're lower level than the monster, you get a penalty to hit. The GM should be sure to throw in some monsters of tiers higher/lower than the heroes occasionally so they can feel like they're growing in power ("Wow, these giant rats sure are a lot easier to kill now!").

Autohits become possible only if three of the four conditions are met:
(A) The target is not armored
(B) the attacker is using a particularly effective weapon
(C) the attacker has "combat advantage"
(D) The attacker is a tier of play higher than the defender

And frankly, if you're a naked goblin facing a Hero who's flanking you, its time to run away anyways. Likewise, if you're a naked first level fighting man and an ancient red dragon is bearing down on you, it is also time to depart expeditiously.

"But, what about..."
All of these rules are optional to add extra depth.

What about shields?
Giving a +1 bonus to AC (i.e., about a +3 bonus in D20 terms) is too much. Thus this simple rule:
Once per encounter, you can use your shield to parry an attack that hits you. Treat the attack as having missed altogether. Normally a shield gives +1 or +2 to AC. That translates to 5-10% fewer hits. In a typical 7 round combat, the fighter will be taking about 14 hits (assume he gets ganged up on some). If he uses a shield, you can expect 1-2 of those hits to miss due to the shield. So, allowing him a "dodge" replicates this nicely.

You can also add a modifier like this:
Defender is parrying with shield: -2 to hit, adjacent character gains -1 to be hit as well

What about leather armor?
Why would you wear light armor if you don't get an AC bonus?

First, there might be magical versions. This is of course handy.

Second, you could use something like our shield rule above, and let a player dodge an attack 1x/encounter.

Finally, you could deal with it on the wounds side. Perhaps leather soaks 1 Hit, chain soaks 2 Hits, and Plate soaks 3. Its better to have Soak 1 from leather than Soak 0 from nothing.

What about critical hits?
Having a critical hit occur 15% of the time (any natural 6) is probably too much. Indeed nearly 1/3 or 1/4 of hits would be criticals if you allowed them on any natural 6, which would make combat very swingy. Ideally you want criticals to occur on about 5-10% of attack rolls.


ADVANCED CRIT RULE:

Any natural 6 indicates a critical threat. Roll 2d6 to confirm the critical. If the result is <= 4 +/- your HEART modifier, you score a critical hit. - If your natural 6 would have hit the target, you deal maximum damage. - If your natural 6 would not have hit the target, you deal normal damage. Thus, a character with average HEART would score critical hits on about 27% of threats (4.5% of all to-hit rolls). A character with above average HEART (+2) scores crits on about 58% of threats (9.6% of all to hit rolls). Unfortunately a character with really cruddy HEART just about never scores a critical hit.


SIMPLER CRIT RULE:

Any natural 6 on a to-hit roll indicates a critical threat. Immediately make a HEART/CHA check (i.e., TN =4-6, add your current HEART ability score check modifier to the roll). Success indicates a crit that deals maximum damage. A character with Normal Heart will score crits 1/2 of the time on a threat (~8% of all attacks). A character with Superior or Extraordinary Heart will score crits 4/6 the time on a threat (~11%). A character that has had their morale shaken and is badly rattled (say, -2 to Heart checks) will score crits 1/6 of the time (3% of the time).


SIMPLEST CRIT RULE:

Any natural 6 on a to-hit roll indicates a critical threat. If the damage rolled is an odd number, the damage is maximum damage instead. This is much faster as no extra die rolls are required -- you're rolling damage anyways!

Thus, crits occur about 7.5% of the time.

CRIT OPTION: Advantage, PC
When a PC scores a critical hit, they deal 1 hit of extra damage for each tier of play.

What about Magic?
Magic items can be dealt with in several ways.

UNIQUE ITEMS: The first is to treat them like Sting. Attach a situational benefit to it and make each magic item unique. Perhaps it glows near orcs and always grants its owner Combat Advantage against orcs (or is always treated as being against a favorable armor type).

OCCASIONAL LARGE BONUSES: The second way is to give a major bonus once in awhile (not every round), like our shield rule above . For example, a +1 sword meant +5% hits. In a typical 7 round engagement, that means about a 35% greater chance to land a hit over the course of the fight. So, over the course of the day, it pretty much meant one extra hit. So, you could just say that a +1 magic weapon either automatically hits 1x/day, or it grants +2 to hit 1x/encounter.

THE ARMS RACE -- YOU'RE JUST TREADING WATER ANYWAYS: However, consider that monster AC usually increased to counter the increase in PC power. So, a magic sword might not really increase the odds of hitting; it might just allow a PC to keep pace with the arms race. So you could say that a magic sword didn't really give any real mechanical benefit, and go back to option 1 -- make the magic flavorful!

YOU ONLY GET A BONUS TO HIT FOR THE LAST ADVENTURE IN A TIER: You could reserve granting +1 to hit or +1 to AC for only the most powerful of items. This would be like your top-of-the game Holy Avenger class of weapons. Sure it skews the odds but it won't be around too long. You could minimize the stacking by not allowing this bonus to stack with either Combat Advantage or Armor Type Vulnerability. You could also allow a Tier 1 Magic Sword to grant +1 to hit vs Tier 1 monsters, but no bonus vs. Tier 2 monsters. Thus you can hand it out a few sessions before your players go into Tier 2 and not destroy the game because its basically a consumable item.

DEAL WITH IT IN THE WOUNDS SYSTEM: Finally, you could allow magic weapons to deal more wounds. The wound system might be a bit more granular, so a +1 weapon that deals +1 wound would still allow a character to emphasize their offense. Likewise +1 armor could soak 1 wound damage.