All you have to do is launch the game and if the Black Screen issue persists, press ALT Enter.
This will bring the game in Windowed mode and the issue will be resolved.
Buddies were also an important part of The Stick of Truth, but Ubisoft San Francisco is working to expand their roles for the sequel in a number of ways.
"We wanted to get more of the buddies voices and their powers in there," says senior producer Jason Schroeder.
Try to update your GPU drivers and the issue should resolve.