NPC

Merchants
"Asylum"Snuggly the Crow

Unlock: when you return to the Asylum"Firelink Shrine"

Petrus
Unlock: He's at Firelink from the start near the graveyard area

Sells the same items

Laurentius
Unlock: In the Blighttown swamp you must save him from a butcher/dogs near where the old bonfire was in the round area where a dragon scale used to be

Sells the same items

Logan
Unlock: Free him from his cage as usual in Sen's

Also sells Great Magic Weapon

Domhnall
Unlock: Open the door at the top of Sluiceworks and he's just to the left where the old depths bonfire used to be

Sells the Weapon Smithbox for 2,000 instead of the Bottomless Box

Doesn't sell the Master Key

Now sells Standard/Large/Wooden Arrows and Standard/Heavy/Wood Bolts

Sells the Xanthous Legs and Gloves

Patches
Unlock: Complete his quest in Undercrypt and go down the steps to where Petrus of Thorolund is standing and make a sharp left, he is squatting near the pair of skeletons on the cliff edge. Note: Specific conditions for his arrival are unknown

Doesn't sell the Eye of Death

Sells a Sunlight Elixir instead of a Divine Blessing"City of the Undead"

Undead Moss Merchant
Unlock: In the old Capra Demon boss room with a bonfire

Also sells a Green Moss Clump for 1,500 souls"Allfather's Parish"

Oswald
Unlock: At the bottom of the Garg's tower as usual

Doesn't sell Karmic Justice

Doesn't sell Bloodbite/Poisonbite Rings

Sells Cursebite Ring

Sells Velka's Rapier

Reah
Unlock: Complete her quest line in Tomb of Giants by defeating her hollow body guards. Then she appears in Undead Parish near the old Lautrec prison cell

Sells a Sunlight Elixir instead of a Divine Blessing

Crestfallen Merchant
Unlock: Near the old bonfire location, drop down from above

Sells the Composite Bow for 12,000 instead of the Balder Shield

Doesn't sell the Catarina set

Doesn't sell any rings"The Old Wilderness"

Dusk
Unlock: Defeat Moonlight Buttferly. Dusk is at the top of the tower afterwards

Sells the same items"Oolacile"

Elizabeth
Sells the same items

Chester
Unlock: He's by the elevator down to the abyss just outside of the Artorias fight

Gough
Also sells Sen's Ember for 30,000 souls"Fetid Slagmire"

Shiva
Unlock: Join the Forest Hunters Covenant with Alvina in the Darkroot Garden. Then talk to him near Alvina in Darkroot (He's about 100 ft from his normal spot, just a little further away). Then he will appear in Fetid Slagmire on the wooden platform next to the elevator up.

Sells the Fire Light Crossbow for 20,000 souls instead of the Demon Great Machete

Also sells the Dark Wood Grain Ring for 30,000 souls

Quelana
Unlock: Have a +10 pyro flame or greater in your inventory

Sells the same items

Eingyi
Unlock: Have the egg head effect. Once talking to him with the egg head he will give you an Egg Vermifuge and his shop will be available for the rest of the playthrough, regardless of egg head status.

Sells the same items"New Londo"

Ingward
Unlock: In New Londo on the rooftop as usual

Sells the same items

Kaathe
Unlock: Join the Darkwraith Covenant before placing the Lordvessel

Also sells the Red Sign Soapstone for 100,000 souls

Blacksmiths
"Dead City of New Londo"Griggs of Vinheim

"Sen's Forge"

Andre
Unlock: Now located just inside of Sen's Forge

Doesn't sell the Crest of Artorias

Doesn't sell the Armorsmith Box or Weaponsmith Box

Also sells the Halberd

Doesn't sell any of the 3 shields that he normally sells (Large Leather Shield, Tower Kite Shield, Caduceus Kite Shield). Instead he now sells Warrior's Buckler (800), Scimitar (600), and Kite Shield (1000)

Also sells the Chain set

"Bone Chimney"

Vamos
Located in the same area as the vanilla game.

Drops: Royal Helm, Hammer of Vamos, & Chthonic Spark (if given to him)

"Royal Cathedral"

Giant Smith
Located in the same area as the vanilla game.

Tip: You can get the chest next to him without killing him by sticking to him on his left or wait until the raid where he'll stand up.

Solaire
Annor Londo - In the usual spot on the staircase before O&S

Izalith - His sign appeared when coming from Centipede with the door closed. Just after the dark underpass on the right behind the bottom of the stairs.

Witch Beatrice
Moonlight Grove - Her summon sign is in the same area as the vanilla game, before the Moonlight Butterfly + Walking Bastion boss fight.

Dead City of New Londo - Her summon sign is located below the bridge to the Four Kings white fog. (She must be summoned first in the Moonlight Grove before her summon sign appear)

Note: If her summon sign did not appear, just simply quit out and rejoin again.

Maneater Mildred
Blighttown swamp - Kill her in her invasion and then she can be summoned before Quelaag as usual

Iron Tarkus
Iron Golem - Just above the entrance to Iron Golem where you fight the boulder throwing Giant. In a corner behind some boulders

Maneater Mildred
Fetid Slagmire

invades in the usual place near the old bonfire location. Can be summoned afterward for Quelaag

Sellsword Tishana
Wields a Voltaic Iaito and wears the Shadow set

Blighttown

Invades where the lower moving bridge is near the main entrance

Sen's Forge

Invades just after crossing the swinging axe bridge with the suicidal snake

Paladin Leeroy
The Undercrypt

Invades when you go out onto the ledge where effigy shield used to be

Kirk
Sluiceworks

Invades in the curse frog area as you go toward the humanity above the Worker's Key that requires a jump

Fiery Cascades

Invades when you go to the end of the long hallway with lots of worms where the fire ember used to be near the new bonfire

Izalith

Open the chest where the Chaos Fire Whip used to be (now nothing) and he'll invade you right after.

Depraved Apostate
Wields a Morning Star and shield as well as a talisman for casting Force. Wears the Priest set with a Darkwraith Helm

Does not invade if Petrus is killed

Allfather's Parish

Invades near the Firekeeper's soul by the boar

Bone Chimney

Invades as you come upon the crystal lizard in the room full of necromancers

Drops: A Sunlight Elixir, a Cracked Red Eye Orb, and a Humanity

Marvelous Chester
Descended Township

In the large cathedral in Township

Wicked Delys
Cloister of Exiles
 * At the labyrinth below the well full of skeletons.

Siegmeyer

 * He will be sitting on a ledge before the gates to the depths coming from Blighttown (optional?)
 * In Sen's Forge at the second ball track you must roll off of the edge to the left onto a wooden platform (optional?)
 * He will be in Anor Londo and is hard to miss. To progress you have to kill the 2 Silver Knights blocking the way and talk to him again
 * After that he will be at the bottom of Blighttown before the entrance to the Great Hollow/Ash Lake. To progress you have to give him a purple moss clump and he will reward you with a red and a green moss clump
 * Now he will be in Lost Izalith ready to jump into the poison pit as usual. The same mechanic seems to apply where you must keep his health high to continue his quest. Talk to him once he sits down and warp out. Watch out for the Jeremiah fight here as well.
 * Free Seglinde from the golden golem in The forest area of The Duke's Archives. Then talk with Sieglinde at Firelink and after that both will be in Ash Lake near the first bonfire. As a reward you get the Catarina set and the Pierce Shield.

Lautrec
Drops: Ring of the Embraced
 * Imprisoned in New Londo Ruins. He can be freed with the Sinner's Key from Bone Chimney, or he will eventually free himself
 * Will Kill the Firekeeper in Firelink as usual if he is allowed to live
 * You can pick up the Black Eye Orb and the Dingy set as usual from the Firekeeper's old location
 * Invade Lautrec with the Black Eye Orb in Anor Londo in the area that previously had Havel's set below the secret fireplace entrance
 * The Embraced set is located on the top floor of the room with may dragon head trophies

Havel
Reward (by completing the quest): His set and ring. (by killing Havel: Dragon Tooth and Havel Greatshield. Can't get everything in the same playthrough.)
 * Either kill Priscilla to get her soul or get the Crossbreed Dagger at the bottom of Sen's Forge. (dagger required for Velka pact)
 * Die the scripted death to Seath.
 * Free Havel from his cell at Seath's prison and open the Giant Door. (wait for him to teleport away so it doesn't bug)
 * Go fight Seath in Crystal Cave and hit him with the Crossbreed Dagger, which will make him flee to Ash Lake
 * Havel will kill the Stone Dragon and Seath. (Seath's Lord Soul will be at his boss room at Crystal Cave)
 * Reset the area again and Havel's loot will be spread near the Stone Dragon bonfire.