Need some information please

Hey, great game. I have been playing a lot and got 96 yesterday. Just wanted to know how high is the chance to get the dark sword from the ice dragon. I killed him over 60 times but i still didnt get it. Do i have to be in dark difficulty? Or at a certain stage? Hope someone knows. Thanks

You need to play at dark difficult for the datk weapons and set and inferno difficult for the inferno weapons and set the chance of drop is pretty low put they drop only at this difficults so don't loss your patience :)