The Shadowbreed is a special ability that can be used from every player when he reach level 205. There are 3 different versions from each Shadowbreed for every breed.
You need one of the following Items to get this ability:
Omni: File:215445.pngThe Darker Side Dropps from the Custodians in Inferno (Sorrow)
Neutral: File:215443.pngThe Unknown Path Dropps from the Custodians in Inferno (Sorrow)