Extended Ability Score Modifiers Table

DCC's table for stat modifiers ranges from 3 to 18. There are obvious circumstances where stats can go below 3, those being damage and all kinds of burn (luck burn, spellburn, and the more obscure battle rage) but the book simply doesn't cover what happens to your modifiers. Maybe they can't go below 3? Well, it mentions what happens when they hit zero, so it just seems to be an oversight. Stats can increase too, and some monsters call for opposed checks with greater scores, so what about scores over 18?

Here's the chart I use, ranging from 1 to the obscenely high 40. Below the chart is an explanation of how I arrived at these numbers.

∗ ∗ ∗

Score	Mod	Score	Mod	Score	Mod	Score	Mod
1	-5	11	none	21	+5	31	+10
2	-4	12	none	22	+6	32	+11
3	-3	13	+1	23	+6	33	+11
4	-2	14	+1	24	+7	34	+12
5	-2	15	+1	25	+7	35	+12
6	-1	16	+2	26	+8	36	+13
7	-1	17	+2	27	+8	37	+14
8	-1	18	+3	28	+9	38	+14
9	none	19	+4	29	+9	39	+15
10	none	20	+5	30	+10	40	+15

... and so on, adding +1 per two points ad infinitum.

For scores 5 or less:

Strength: Can carry shield or weapon, but not both.
Stamina: Takes double damage from poison and disease.
Intelligence: Cannot read or write.

When scores hit zero:

Strength: Unable to move.
Agility: Unable to move.
Stamina: Unconscious.
Personality: Incapable of thought or action.
Intelligence: Incapable of thought or action.
Luck: Constantly subject to frequent and bizarre mishaps.

∗ ∗ ∗

And here's how I reached these numbers:

The base DCC rules cover all possible starting scores, 3-18.

Each point someone is reduced below 3 - the literal human lower limit - should be significant, so each one drops the modifier 1 further until incapacitation.

18 is also a limit, the natural human peak. Breaking this is significant, so 19 should come with an increase of 1.

Ogres are defined in the Monsters chapter as having 22 Strength with a +6 modifier. Interestingly, this conflicts with an extended modifiers chart provided in MCC, but we're going to ignore that. Technically MCC is a different game anyway. 

Elsewhere in the Monsters chapter, opposed Strength checks are called for at 20 Strength (Water Elemental) and 24 Strength (Minotaur). There are others which don't specify a score or modifier, so they aren't useful to us. Since the book specifically calls these numbers out, we can deduce that their modifiers must be different than the Ogre's and from each other, but their modifiers are unspecified. We'll just place them up and down by 1 compared to the Ogre - it fits, and we can justify it with the next observation.

The Primeval Slime specifies a score of 12 + 2 per 5' section. 12, 14, 16, 18, 20, 22 and 24 are all already defined as having different modifiers, so if we extrapolate with the assumption that each defined Strength score must have a different modifier, every second point should increase the modifier. I admit this one is a bit of a stretch, but it's a rule consistent with defined values.

The only numbers left uncertain are the odd ones. We have to make it up from here, so I will rule that 21 is +5 because this makes the curve after breaking the natural human limit slightly less steep.

30 sits at a nice round +10. This isn't meaningful, the numbers just line up nicely.

Continuing this up into godlike numbers, I feel like it makes sense to have another peak at double the natural human limit (36). Think of this as breaking a second limit. 3-18 is human, 19+ is superhuman. 36 is reaching deific levels, and sits slightly above the values given in Deities & Demigods back in 1980 (which were maybe a little low for literal gods). As such, 36 and 37 are treated like 18 and 19, and each have a modifier increase. This also puts the first point past double-human at a level where, in a contest, it would take two dice chain movements for the average inferior being to have any chance of success. That seems reasonable for man vs god.

From here onward we continue the pattern of +1 per 2 points forever. I can't think of any further meaningful breakpoints past this and these numbers are already absurd anyway. For the most part, you probably shouldn't even bother giving creatures this powerful any stats.