Esker
Hero
@TwoSix , @Esker :
Since you both were looking to options for GWF, how about this:
If you roll a 3 or lower on a damage die, you can roll an additional die and add it to your damage. If you are rolling more than one dice, you only apply this benefit to one die.
If I got everything right, I think this will result in:
d8: 4.5 -> 6.1875 (+1.6875)
d10: 5.5 -> 7.15 (+1.65)
d12: 6.5 -> 8.125 (+1.625)
2d4: 5 -> 6.875 (+1.875)
2d6: 7 -> 8.75 (+1.75)
So, this grants a bonus a bit less than Dueling's +2. Of course the biggest gain is for the DBS since it does 2d4 and the one die will usually roll 1-3. In this way, it is almost effectively increasing the DBS to 3d4.
To me it feels a bit weird to make rolling a 1,2 or 3 lead to a better outcome than rolling higher numbers. Of course, GWF does that already with 1s and 2s compared to the other values that are below average, but at least rolling high values are better than rolling low values.
Your math is also off for 2d4 and 2d6. You seem to be assuming a 75% chance of rolling a 3 or below when rolling 2d4 and a 50% chance of rolling 3 or below when rolling 2d6, but since you're rolling two dice you have two chances to trigger a reroll, for a (1 - 0.25^2) = 0.9375 chance of rolling a 3 or below with 2d4, and a (1 - 0.50^2) = 0.75 chance of rolling a 3 or below with 2d6. That makes the expected values of these rolls
2d4: 5 -> 7.34 (+2.34)
2d6: 7 -> 9.63 (+ 2.63)
which makes 2d4 better than 1d10, and 2d6 even more better than 1d12 than it already is.