Did vin diesel dislocate is shoulders in the movie pitch black?
From what i've come across, yes, he did actually dislocate his shoulder or shoulders out and back in that scene, they did or they were going to use special effects but they didn't or DID, i don't know. If he really did, that was BADASS
Does Vin Diesel's twin brother fill in for him on set?
No. Vin Diesel's twin brother looks NOTHING like him. They barely look related.