Hatred of THAC0

OK. Confession time.

I hate THACO.

It was a dumb mechanic in 1st Edition AD&D. It remained a dumb mechanic in 2nd Edition AD&D. And ditching it in Enroth would make make it easier to learn and play. THAC0 has a number basic problems:

1. It's confusing. I've played D&D for decades and still have to think about it every single time.
2. It adds a new type of "adjustment" to a system that already has to many, for no reason. As an example: what is the actual difference between "reducing THAC0 by one" and "a +1 'to hit' bonus". Answer: none whatsoever.
3. It's makes the game inconsistent: it creates a system where high numbers are good in some situations and bad in others. Again, for no reason. Similarly, getting a '+1' is usually good... unless you mean AC, when it is bad. Unnecessarily complicated.

One of the best things done in 3E was the elimination of THAC0. The technique used to do so could also be used in Enroth, in such a way that a) the system is easier to follow, b) results in the exact same chance to hit as the current system, and c) scales better.

Problem

The math in the current system basically works like this:

Let R be the number you rolled.

Let T be the total 'to hit adjustment' from magic equipment, etc.

Let H be the number needed to hit. If you roll (R + T) ≥ H, you hit.

Let L be an adjustment based on skill level.

H = THAC0 - AC

THAC0 = 20 - L:

Knight/Paladin/Archer (bow) L = (skill level-1)

Archer (other)/Cleric L = (2 * (skill level-1))/3

Druid/Sorcerer L = ((skill level-1)/2)

AC = 10 + A, where

A = negative bonus from armor - (armor skill-1)/5 - AC adjustments*

• Note that AC adjustments (e.g. +5 plate) make a target harder to hit, so they must be subtracted. This makes AC decrease. Since AC is subtracted from THAC0, this makes H increase.

Note that A is always a negative number.

So, a Knight with a level 3 weapon skill against a target with studded leather and 6 levels of skill in it, with no other modifiers to either:

H = (20 - 2) - (10 + (-3 - 1 - 0)) = 18 - 6 = 12 (i.e. 60% chance to hit)

What happens here is that there is a relatively complicated formula to figure out the "target number" (H), using both positive 'penalties', negative 'penalties', positive 'bonuses' and negative 'bonuses', depending on what is being adjusted. There is also an adjustment to the roll itself.

Solution

What 3rd edition did was to tweak this idea a bit by making two simple changes:

1. Change the dynamic to a roll (modified by an adjustment) vs. a target number (also modified by an adjustment).
2. Make all adjustments positive numbers.

This seems like no difference at all really, but it makes resolution a lot easier to understand.

Note one thing here:

R + T ≥ H

R + T ≥ THAC0 - AC

R + T ≥ (20 - L) - (10 + A)

R + T ≥ 20 - L - 10 - A

R + T ≥ 10 - L - A

R + T + L ≥ 10 - A

Now, remember that A is always a negative number, because AC "bonuses" are negative numbers. But what if you change that? What if bonuses are always positive numbers and penalties are always negative and a higher AC is better than a lower one. For example, what if studded leather, for example, gives a +3 AC bonus instead of a -3 AC bonus? Well, then the sign of A flips, and you get:

R + T + L ≥ 10 + A

That is:

• Your roll (R)
• ...plus any to hit bonuses (T) (from magic or the like)
• ...plus adjustments from your level (L)
• must equal or exceed ten
• ...plus adjustment from armor
• ...plus adjustment from armor skill

The math is actually completely the same, but you can explain the above to anyone, and they will understand and remember it within 30 seconds.

Even Better

Something else interesting happens here as well. The result is basically a roll, plus stuff that helps the player, against a target number that is scaled for difficulty. In short, what you have here is a universal mechanic. In combat, the target number happens to be based on AC, but there is no reason that other types of tests couldn't be based on something else. Want to find a secret door? Roll, add your skill (perception or the like, maybe an attribute benefit) compare to a difficulty number (ten plus some modifier for how well concealed the door is).

Something else comes out of this as well: it is easier to scale things for the PCs. At any given level, the PC is likely to have a certain bonus available from skill level and equipment, plus or minus a few. Knowing that, you can easily figure out what AC or other targets will present a challenge to that PC.

To convert Enroth to use this idea, all you need to do is:

• Eliminate all mention of THAC0
• Set starting skill bonuses (for lvl one, untrained characters) to zero.
• Set starting AC bonuses (for clothing) to +0.
• Switch the sign the bonus intrinsic to the type of armor.
• Instead of skill levels subtracting from THAC0, they add.
• Instead of armor levels reducing AC, they add.
• Change the mechanic from figuring out the number needed to hit to instead focus on the adjustments made to the roll and the adjustments made to a base target number.
• Change the concept of saving throws to use the same mechanic (i.e. roll, plus bonus from attributes and so on vs. difficulty).