MyD20 Lite: The Math Behind The Monsters, Part One...

Good Morning, All:

Today, I wanted to start explaining the math behind MyD20 Lite, in regards to monster statistics. This may, of course, cause some changes in the final values I use, since I'll also be exploring some of the comments that have been posted about the math. I do want the game to be fun, after all. In order to start off, I should probably start off with a list of my general assumptions.

1. I assume that, by 4th level, characters will have a +1 bonus to Saves, Attacks, Damage and AC due to magic items. This increases by +1 every four levels (i.e. +2 at 8th, +3 at 12th, and so on.)
2. I want to tie the basic math behind monster stats to Hit Dice, so that it is easier to translate pre-3E creatures to MyD20 Lite, as they frequently do not have ability scores.
3. I assume that I can use Bad Axe Games' Trailblazer tables to assign a rough character level to each hit die value, so that I can tie character advancement to a monster's abilities.
4. Using the Priest's attack rolls at each character level, including magic adjustments, and assuming that the average monster probably should require about a 10 on the D20 to hit it, I can determine the base AC for a given Hit Die value.
5. Assuming the best save progression at each character level (+CLM+2), and assuming that the character should roll a 10 or higher on the D20 in order to successfully save, I can determine the base DC for special abilities for a given Hit Die value.
6. Using the Priest and Rogue as the median character in terms of hit points, it is possible to calculate the number of hitpoints an average character can have at each character level.
7. I assumed that the average encounter will last three combat rounds, and should determine numbers aimed at that as a goal.
8. I assume that a monster will likely hit its target once a round, or twice a round at best, with physical attacks.
9. A suggested minor damage value can be calculated from the base hitpoints for a character of the appropriate level such that four average uses of that damage should disable the average character. That value can be converted to a given die type (with preference towards d6s). When dealing with fractions, round down so as to favor the character.
10. A suggested moderate damage value can be calculated as per minor damage values, save that only three average uses of that damage should disable the average character.
11. A suggested major damage value can be calculated as per minor damage values, save that only two average uses of that damage should disable the average character.
12. A suggested minimal damage value can be calculated as half that of the moderate damage value, creating a damage value that should disable the average character in six average attacks. This value should be used for ongoing damage, such as poison effects.

Let's start with the basic values for a PC, which will be used for comparison and calculation.

Table: Base PC Values

PC Level	Avg HP	Avg BAB	Magic Adj	Best Save
1	16	+0	+0	+2
2	21	+1	+0	+3
3	26	+2	+0	+3
4	31	+3	+1	+4
5	36	+3	+1	+4
6	41	+4	+1	+5
7	46	+5	+1	+5
8	51	+6	+2	+6
9	56	+6	+2	+6
10	58	+7	+2	+7
11	60	+8	+2	+7
12	62	+9	+3	+8
13	64	+9	+3	+8
14	66	+10	+3	+9
15	68	+11	+3	+9
16	70	+12	+4	+10
17	72	+12	+4	+10
18	74	+13	+4	+11
19	76	+14	+4	+11
20	78	+15	+5	+12

Now, to link monster Hit Dice to character level, we look at the Trailblazer tables for the average number of Hit Dice at each CR (assumed to be equal to character level), find the slope of those values to determine a consistent power curve for Hit Dice versus character level, and use that to calculate the following values:

Table: Base Character Level by HD

Monster HD	Character Level
1	0
2	1
3	2
4	3
5	4
6	5
7	6
8	6
9	7
10	8
11	9
12	10
13	11
14	12
15	12
16	13
17	14
18	15
19	16
20	17
21	18
22	18
23	19
24	20
25	21

Today, I'll cover DCs for special abilities, since that's pretty easy to determine from the basic information above. In essence, I can find the DC for a given character level by adding the Best Save value and the Magic Adj value from Table: Base PC Values to a base of 10, since that's what I want them to roll. In the table below, I used those calculations to determine a rough base, and then smoothed the curve out over the range of hit dice, for a more regular procession.

Table: MyD20 Lite Monster Save Progressions

HD	Level	Rough DC	Smoothed DC
1	0	12	12
2	1	12	13
3	2	13	13
4	3	13	14
5	4	15	15
6	5	15	15
7	6	16	16
8	6	16	16
9	7	16	17
10	8	18	18
11	9	18	18
12	10	19	19
13	11	19	19
14	12	21	20
15	12	21	21
16	13	21	21
17	14	22	22
18	15	22	22
19	16	24	23
20	17	24	24
21	18	25	24
22	18	25	25
23	19	25	25
24	20	27	26
25	21	27	27

As you can see, I already have to make some adjustments to the rough draft as a result of this discussion. It's a Good Thing(tm) that I'm going through this exercise then, isn't it? We'll continue tomorrow with AC and damage.

Hope This Helps,
Flynn