Excelsior Endeavor started as my take on the TSR Marvel Super Heroes game using a d6 mechanic. It was initially leaning in a very "clone" direction, but since then I've veered off in multiple directions, such that this idea does not currently have a solid, defined end I'm currently headed for. For now, I'll just document what I have and some thoughts as they form up.
The initial idea is that you have Attributes that are rated from essentially 1 through 15. Ratings of 1-5 are humans scale, 6-10 are super-scale, and 11-15 are cosmic scale. The tentative benchmarks were set around where the TSR Marvel Super Heroes game sets them. To resolve tasks you basically roll a number of d6 equal to your Attribute Rating, plus a "Null Die" of a different color. Any roll of a 6 on a die counts as a level of success. Should the "Null Die" roll a 6, you are granted a level of success and get to roll that die again, gaining a level of success for each time it is able to roll a 6. Should no dice roll a 6 and the "Null Die" roll a 1, then the attempt is considered a fumble. Then, the idea is that each level of success was similar to success levels in TSR MSH, with 1 level being equivalent to a Green Result, 2 to a Yellow and 3 to a Red Result. Any success levels above 3 were then applied to the effect. For example, in TSR MSH if you have a Good Strength and successfully punch someone, you'll do 10 damage on a Green Result, with Yellow and Red giving you the ability to Slam or Stun the opponent. Under this scheme, if someone scored 4 levels of success, it would be the same as a Red Result, but also the damage would be bumped up a column to Excellent (20 damage). You can see how all of the default assumptions here are from TSR MSH, just swapping in this die mechanic and allowing for results that are higher than Red. It is statistically pretty OK and has the advantage of getting rid of the chart, but allowing you to basically keep the rest of the game if you so desired. Thing is, I don't know for sure that that's what I desire. In any event, below is a table of the probabilities under this system.
Levels of Success
Dice 0 1 2 3 4 5 6 7 8 9 10 11 12
1 83.33 13.89 2.31 0.39 0.06 0.01
2 69.44 25.46 4.24 0.71 0.12 0.02
3 57.87 32.79 7.78 1.30 0.22 0.04 0.01
4 48.23 36.97 11.95 2.38 0.40 0.07 0.01
5 40.19 38.85 16.12 3.97 0.73 0.12 0.02
6 33.49 39.07 19.91 6.00 1.27 0.22 0.04 0.01
7 27.91 38.14 23.10 8.32 2.06 0.40 0.07 0.01
8 23.26 36.44 25.61 10.78 3.10 0.67 0.12 0.02
9 19.38 32.24 27.41 13.25 4.38 1.08 0.21 0.04 0.01
10 16.15 31.76 28.55 15.61 5.86 1.63 0.36 0.07 0.01
11 13.46 29.16 29.09 17.77 7.48 2.33 0.57 0.12 0.02
12 11.22 26.54 29.10 19.65 9.20 3.19 0.86 0.19 0.04 0.01
13 9.35 23.99 28.67 21.23 10.94 4.19 1.25 0.30 0.06 0.01
14 7.79 21.55 27.89 22.47 12.66 5.32 1.74 0.46 0.10 0.02
15 6.49 19.26 26.83 23.37 14.29 6.54 2.34 0.67 0.16 0.03 0.01
16 5.41 17.13 25.57 23.95 15.80 7.83 3.04 0.95 0.25 0.06 0.01
17 4.51 15.17 24.16 24.22 17.16 9.16 3.84 1.30 0.37 0.09 0.02
18 3.76 13.40 22.67 24.21 18.34 10.49 4.72 1.72 0.52 0.13 0.03 0.01
19 3.13 11.79 21.12 23.95 19.32 11.80 5.69 2.22 0.72 0.20 0.05 0.01
20 2.61 10.35 19.57 23.48 20.09 13.05 6.71 2.80 0.97 0.29 0.07 0.01
21 2.17 9.06 18.03 22.83 20.66 14.23 7.76 3.45 1.28 0.40 0.11 0.03 0.01
% of Fumbles
Dice
1 16.67
2 13.89
3 11.57
4 9.65
5 8.04
6 6.70
7 5.58
8 4.65
9 3.88
10 3.23
11 2.69
12 2.24
13 1.87
14 1.56
15 1.30
16 1.08
17 0.90
18 0.75
19 0.63
20 0.52
21 0.43