Undead Merchant (guy)- The undead merchant is located in the undead burg close to the first bonfire in that area. There's a set of stairs guarded by two spear carriers. the stairs going down are kinda hidden by some smashable boxes. After you go down stairs you see him in a room directly across and to your right. Undead Merchant (lady)- She can be found in the lower parts of the undead burg. As you progress through the lower sections of the undead burg you'll see a tower you can go in that spirals go up it until you see a door go inside to enter an aqueduct now look right to see the merchant shes behind some bars. also if you go right you can open a door that leads to the firelink shrine. Crestfallen Merchant- This merchant is in sen's forest and sells upgrade stones. When your close to the boss area at the rooftops basically you should notice a broken path. Jump it and go inside the building to find the merchant. Shiva Merchant- Shiva will only be a merchant for you if join the forest covenant. Join the covenant and talk to him in the forest. Now go to blight town and reach the big wheel and he will be leaning at the base of the contraption. he sells some pretty good weapons. If you leave the covenant he will not sell to you anymore. Domhnall of Zena- You first see him in the depths afterwards hell will appear under the aqueducts in the firelink shrine area. He will sell the boss's Ornstein or Smoughs armor after you defeat them.