Quote Originally Posted by goldfinch View Post
What are shadow rear derailleurs?
Instead of sticking out to the right, the body of the derailleur tries to hide "behind" the cassette. The intent is to reduce the chance that the derailleur might get snagged on something next to the trail.

The shift cable also is rerouted to eliminate the 180 degree loop entering the derailleur. This also reduces the chance of snagging something.