How do you get the Rider in Borderlands?

Answer 1

Once you get the mission Another Piece of the key, or puzzle, or whatever it's called, Follow a path to the back of Marcus's store, or next door to that, and stand in front of the door. (this location is right under the Repair Kit you found earlier) The door should open, revealing an elevator going down. The lift will take you down1 floor and stop, leaving you to battle 6 lvl 30 Psycho's. Once dead, there should be a white weapon case, and a red one. The White case will contain additional weapons, as the Red one will contain the Rider, referring to the BB Rider from a Christmas Story. you'll also find the leg lamp from the movie too. The Rider is a sniper (i think) and it's stats vary everytime you do this. You can repeat the process by leaving New Haven, and returning. Note: This trick will stop working once you complete your plot mission. I highly recommend doing this on Playthrough 2, because the Rider will be 4 times as strong, but I am unsure of how strong the Psychos are. So choose carefully.

The Psychos on Playthrough 2, the Psychos are level 42, unless you've beaten playthrough 2. If you have, you can't get the rider at all.