Dice Mechanics: Examples

Marvel Superheroes

         TSR's Marvel Superheroes game uses a universal table that makes fairly clear what the probabilities are. What is important for some people is that the table uses percentile dice and a look-up that slows the game down. Alternate dice approaches are therefore considered. The basic result table is given below, along with a text table that shows the chances of each color result.

Rank Value Chance of Result Cumulative Chance
GreenYellowRed GreenYellowRed
Shift 00 30%4%1% 35%5%1%
Feeble2 30%9%1% 40%10%1%
Poor4 30%14%1% 45%15%1%
Typical6 30%17%3% 50%20%3%
Good10 30%22%3% 55%25%3%
Excellent20 30%24%6% 60%30%6%
Remarkable30 30%29%6% 65%35%6%
Incredible40 30%30%10% 70%40%10%
Amazing50 30%35%10% 75%45%10%
Monstrous75 30%35%15% 80%50%15%
Unearthly100 30%40%15% 85%55%15%
Shift X150 30%40%20% 90%60%20%
Class 10001000 30%40%25% 95%65%25%

         Notes that the probability of a Green result is always 30%. Thus, a Yellow or Red result always happens when the minimum success chance is exceeded by 30. The Red success chance is more complex, but is roughly one-fifth of the total chance of (Yellow + Red). Below is a graph of the probability of a Red result as a fraction of all Yellow or Red results. That is, what fraction of (Yellow or Red) successes are Red. The fraction increases from roughly 10% to 38% as the rank increases.

         Som people have had some issues with this roll procedure, because it requires both a double die roll as percentile and a table lookup. One suggested approach for this is to write in the break points for the die roll with each ability. So if you have an ability at Remarkable, then you would write beside it on the character sheet 36, 66, and 95.

         Another option is to simplify the table into a simpler die roll. You could instead roll both 1d20 and a 1d6 at the same time. The d20 is checked against a target number, and if it beats the target number by 6 or more, then it is at least a Yellow Result. If in addition there is a "6" on the 1d6 (or 5-6 for Rank Monstrous and up), then the result is Red. The resulting chances are quite close to the official table, while most likely simpler to implement at the table.

Rank Value d20 Target Official Cum. Chance Simple d6 Chance
GreenYellowRed GreenYellowRed
Shift 0014 35%5%1% 35%5%1%
Feeble213 40%10%1% 40%10%2%
Poor412 45%15%1% 45%15%3%
Typical611 50%20%3% 50%20%3%
Good1010 55%25%3% 55%25%4%
Excellent209 60%30%6% 60%30%5%
Remarkable308 65%35%6% 65%35%6%
Incredible407 70%40%10% 70%40%7%
Amazing506 75%45%10% 75%45%7%
Monstrous755 80%50%15% 80%50%17%
Unearthly1004 85%55%15% 85%55%18%
Shift X1503 90%60%20% 90%60%20%
Class 100010002 95%65%25% 95%65%22%

John H. Kim <jhkim-at-darkshire-dot-net>
Last modified: Thu Aug 4 23:58:31 2011