When striking a foe if you amplify your punch with magic or energy on the exact moment of impact you will get a mystical effect some have labeled as Black Flash depending on how much energy or magic is put into the attack will effect the damage and probability of it working.
On your next hit, the target will be hit with the force of your Black Flash for 1d12 Force damage at a 100% success rate.
When cast at higher levels the damage increases by 1d12 but, the success rate decreases by 12% for each upcast.
Success Rate by Level: 100%,88%,76%,64%,52%,40%,28%,16%,4%
When calculating the percent above 50% just don't roll the number you fail at i.e. if you need 80% just don't roll a 20-1 or its a fail.
When calculating the percent below 50% you need to roll the number you need i.e. if you need 20% you need to roll a 20-1 for it to succeed