Borderlands

Fast travel to Old Haven and follow the left wall after you get in to reach a pile of dead bandits. Notice the glowing bandit or glowing key nearby that starts the quest.

To get the Green Thumb quest, fast travel to the Middle of Nowhere Bounty Board. Get a car from Scooter's and drive to the right. Notice the small shack with big plants around it. Talk to the man leaning against the shack tp get the quest.

Successfully complete the game to unlock New Game+ mode. In your second session, all the enemies will be very powerful.

To score a critical hit on a human, shoot it in the head. With a sniper rifle this usually kills instantly For a Skag, shoot it in the face when its mouth is open. This varies depending on the type. For the pups, shoot them while they roar at you. For adults, quickly shoot them while they jump at you. For the spitters, shoot their mouths while they fire their poison projectile at you. Critical hits are easiest at close range with a shotgun or scattergun.

Start a Co-op mode game. After finding a desired item, drop it on the ground then exit the game without saving it. Have your Co-op partner take the item. Resume the game and you will still see that item on the ground and can collect it. Your Co-op partner can then give you the duplicate item that was previously picked up. This can be repeated as many times as desired.