Dangerous (3.5e Equipment)
From D&D Wiki
A weapon with this property flashes with a disruptive energy that accumulates in both power and the chance of harmful dismissal. The dangerous weapon deals extra damage starting with 1d2 points of damage. With each successful attack, the weapon’s extra damage increases as follows: 1d3, 1d4, 1d6, 1d8, 2d4, 1d12, 2d6, 3d4, 2d8, 3d6, 2d10, 2d12, 4d6, 5d6. Along with the damage increase, a chance of energy dismissal increases starting at 2% and accumulating 2% with each successful attack up to a total of 30%. The d% roll is made along with each attack roll to determine a possible dismissal. The weapon releases its generated energy upon a failed d% roll. The flash of released negative energy deals the weapon’s wielder damage equal to that of its extra damage roll. In addition, its wielder and all creatures within a 20 ft radius of the weapon are blinded for rounds equaling that damage. The weapon resets with each energy dismissal.