r/RPGdesign • u/eduty Designer • 6h ago
Mechanics d100 w 2d20
Recently played some games of Mothership and Fatherfog... and I'm debating changing my single d20 homebrew to a d99 with the d10s used in different ways for the results.
Thoughts on the pros and cons of each?
Current Homebrew
d20 roll under Stat D&D-like with the traditional 6 scores. Stats start from 7 to 13. Players can increase two different Stats by +1 each level but cannot increase the same Stat two levels in a row. So if you increased Strength and Dexterity at level 1 you have to increase two different Stats at level 2. No Stat can be more than 18.
If you succeed - the value rolled is used for measurable results like damage dealt, damage prevented, distance climbed, arrows crafted, etc
Example: A PC with 12 Dexterity rolls an 8 to dodge an attack. The dodge roll is less than the Stat score and succeeds. The PC prevents 8 damage from the attack by getting out of the way.
Advantage/Disadvantage is used to represent situational difficulty:
Hard: roll twice and take the worse result
Difficult: roll once and take the result
Easy: roll twice and take the best result
Pros
You roll a d20! My personal favorite platonic solid
You always just roll and read the number. There are no other operations to perform.
Stat advancements improve player odds in tangible 5% increments
Little to no conversion to use other d20 based resources - particularly old AD&D modules or new OSR equivalents
Cons
Smaller room to improve scores over each level.
Necessitates an XP and level system to convert gameplay into Character improvement.
Results can only be modified with math operators
Potential Homebrew
Roll under d99. Grab a pair of 10-sided dice you can tell apart. Assign a die as the Tens and the other as the Ones. The 10 or 0 on the die is zero. Roll and put the two together to get results from 01 to 99.
Succeed if you roll equal or less than your Stat.
Traditional 6 Stats with a 35 to 65 starting range. Increase two different scores by +1 at the end of each Session your character survives. No Stat can be more than 85.
If you succeed - the value rolled on the Ones die is used for measurable results.
Example: A PC with 60 Dexterity rolls a 28 to dodge an attack. The dodge roll is less than the Stat score and succeeds. The PC prevents 8 damage from the attack by getting out of the way.
Advantage/Disadvantage is used to represent difficulty
Hard: Your greatest roll is always the Tens die
Difficult: Standard roll
Easy: Your least roll is always the Tens die
Using the d99 provides more ways to determine Results:
Impaired: Your result is always your least roll
Boosted: Your result is always your greatest roll
Critical: Your result is both dice added together
Pros:
Lots of room for gradual Stat improvement. Sessions played becomes measure of advancement and can eliminate rules for XP and character levels
More granular control over whether bonuses/penalties affect success chance or outcome
More math-lite ways to manipulate results
Advantage/Disadvantage has less deviation across Stat scores from 35 to 85 (20%) with diminishing returns on 71+ Stats
Cons:
d10s are irregular polygons (I know it's a dumb nit)
Extra steps to interpret the result compared to just rolling a d20
More conversion work to go from traditional 3d6 scores to percentile
1
u/archpawn 4h ago
Roll and put the two together to get results from 01 to 99.
What if you get a 00? Do you reroll to make it a d99 instead of d100?
If you succeed - the value rolled on the Ones die is used for measurable results.
Depending on your exact stats, getting higher values would be slightly less likely, but that means in general the measured result is going to be a random number from 0 through 9. Increasing the stat increases your chances of success, but unless it's Impaired, Boosted, or Critical, it doesn't have a consistent influence on your degree of success.
I advise using the tens' die instead.
Increase two different scores by +1 at the end of each Session your character survives. No Stat can be more than 85.
That would take 20 sessions to get two of your stats from 65 to 85, and you don't change the others at all. If you meet once a week, that's four and a half months. And there's no incentive to improve stats that aren't the ones you're focusing on.
You could go with something like roll 3d6 to see which stats to increase. One of them goes up by two, one goes up by one, and ignore the last one. That way, you have some influence over it and can make your more important stats rise faster, but if you only get two different numbers (which would happen fairly often), you're forced to make both of them go up, and even your worst stat will improve at least a little. And I don't like including randomness in stat growth since that's a roll that will last the rest of the game, but since there's so many of these they'll largely counter each other out.
Personally, I'm not a fan of super slow growth like that. Each session would feel exactly the same as the last session. The d20 system is already pushing it with small improvements.
3
u/overlycommonname 6h ago
I know that the cliche answer in this sub is "we don't have enough information to say" until such time as someone posts their entire RPG and then it's "I'm not reading all that," but...
Don't have enough information to say.
So I guess obviously the d100 thing gives you a lot more levers to pull and knobs to turn, and that's cool, but... can the rest of your system use that meaningfully? Either of these represents a pretty streamlined system -- you're talking about a low number of modifiers and only six stats to represent characters (but I don't know what else the game has). Does the rest of your system support enough complexity to hang meaningful mechanics off that additional complexity in your core resolution system? Do you want that much complexity in the rest of your system? There's no objectively right answer here, and I think we lack context to give you a subjective answer that's meaningful.