copied from the wiki
Towards White
Kill a Demon (boss) in a particular World (+1)
Kill the Red Dragon (+1) in 1-2
Kill the Blue Dragon (+1) in 1-4
Kill the Black Phantom Form of one of the 5 special named NPCs that appear in Pure Black World Tendency
Defeat Black Phantom Executioner Miralda (+3) in 1-1
Defeat Black Phantom Scirvir, The Wanderer (+3) in 2-2
Defeat Black Phantom Lord Rydell (+3) in 3-1
Defeat Black Phantom Satsuki (+3) in 4-1
Defeat Black Phantom Selen Vinland (+3) in 5-2
Defeat a Primeval Demon (+3) (once per world per game)
Defeat Black Phantom NPC (see above) and 1 Primeval Demon without returning to Nexus. (+6) (once per game)
Defeat Black Phantom NPC (see above) and Primeval Demon without returning to Nexus, and then defeat 1 Boss. (+7) (once per game)
Kill an invading Black Phantom
Resurrect a summoned Blue Phantom
Note: To maintain White Tendency after defeating a boss (approx 45% shift to White), then go to the Nexus and commit suicide in the Nexus. Death in body form in a world equates to a (30%) shift back to black tendency, undoing all the effect of killing the boss.
Towards Black
Die outside the Nexus while in Body form (-1)
Kill Old King Doran (-2) in 1-1
Kill the Body Form of one of the 5 special named NPCs that appear in Pure White World Tendency
Kill Body Form Executioner Miralda (-3) in 1-1
Kill Body Form Scirvir, The Wanderer (-3) in 2-2
Kill Blue Phantom Lord Rydell (-3) in 3-1
Kill Body Form Satsuki (-3) in 4-1
Kill Body Form Selen Vinland (-3) in 5-2
just note that every time you sign into the server it changes the tendency to an average setting so if you want it to remain unchanged always play the game in offline mode, however if you just want worlds in pure black then you can always use the dupe glitch to get loads of stones of ephemeral eyes then you can start the game in online mode and just commit suicide a few times in each world to shift them to pure black (wt only resets when you first sign in, any changes you make in online mode will stay until you sign in again) also world tendency changes don't take effect until you return to the nexus so if you kill yourself a few times it will look like nothing has changed until you leave the world and go back in again
the hardest thing to find is pure bladestone, you need to kill the maiden in black after you defeat king alant at the end of the game so if you've not done this first time around make sure you do it next time, give her soul to yuria the witch to learn soul sucker, clear all the levels in world 4 then put it into pure black wt, go into 4-3 then run back into 4-2 until you come up to a black phantom skeleton, walk up slowly so your just behind it and cast soul sucker to kill it instantly and hope it drops a pure bladestone (took me several hours to get one)
http://www.youtube.com/watch?v=z3tmWDmdpHQ&feature=relatedyou can also use this method to rack up loads of souls if you want to level up quickly and it stacks with ring of avarice and soul thirst (if you have enough mp to cast it along with soul sucker) to give you even more souls on each run
you will also need to change character tendency to get the friend and foe rings, you get the friend ring after talking to the monumental while at PWCT so go for this first (i did it the other way around by mistake and it's easier to go to black from white) to shift towards white you need to kill the npc black phantoms in each world or beat any invading black phantom, make sure you deal the final blow as killing them with poison or causing them to fall has no effect, once you're at PWCT go and talk to the monumental to get the ring
to get the foe's ring you have to complete the Mephisopheles side quest, she only appears at PBCT
Towards Black
Invade as a Black Phantom and kill the host.
In any world, use a Black Eye Stone and defeat the host as an invader
Using Blue Eye Stone in the World 3 -- Tower Of Latria. You will sometimes to be summoned by the Old Monk to be a Black Phantom; which will lower your Character Tendency, if you beat the host player. You can keep doing this as many times as you like until your Character Tendency is Pure Black. It doesn't require the killing of NPC's, and is safer than invading with the Black Eye Stone. ( You may use the Black Eye Stone in 3-1 to be summoned by the Monk. Note that this does not mean you will be summoned by the monk the first try, and you do not have to wait to be summoned at 3-3. This has been confirmed by many players. )
You can also "force" the Old Monk to summon you if you use the Black Eye Stone in 3-3. You can use the stone in the small chamber at the bottom of the tower's steps, close to the Maneater Archstone. You may have to move some distance from the Archstone. If the invasion fails, there was no player available to challenge.
If summoned for the Old Monk, your tendency will only change if you actually kill the other player yourself. It's possible that the other player will die getting to you. You may still receive the Monk's Head Collar, but it won't shift your Character Tendency.
Killing four or five harmless NPCs (depending on current Character Tendency) will take you from Pure White to Pure Black. Below is a list of relatively harmless (won't hurt your game if dead) NPCs that you can kill to shift the character tendency.
1-1, 1-2, 1-3 - Dregling Merchant (-2)
2-1, 2-2 - Filthy Man (-3)
3-1 - Once Royal Mistress (-3)
4-1, 4-2 - Graverobber Blige (-2)
5-1, 5-2 - Filthy Woman (-1)
Nexus - Blue Phantom NPC the Crestfallen Warrior (-2). If you don't speak to him, he'll remain in the Nexus for the duration of the game, or until you kill him. If you exhaust his dialogues to "aggh who are you I don't remember" and reload he'll drop a Storied Soldiers Soul.
Nexus - Acolyte of God (-2) & Worshipper of God (-3), make sure you get the Pure Faintstone from her if your faith is at least 20 before you rescue Saint Urbain.
Nexus - Freke's Apprentice (-2). Make sure you have rescued Freke first.
Kill 3 of the special named NPCs. Killing these will also move the World Tendency -3 back towards black.
2-2 Body Form Scirvir the Wanderer (-2). Appears only in Pure White World Tendency
3-1 Blue Phantom Lord Rydell (-2). He has no Tendency requirement to appear, but requires Cell Key from Pure White World Tendency in 3-2.
5-2 Body Form Selen Vinland (-2). Appears only in Pure White World Tendency
i'd recommend reading through the
wiki first especially on the unique weapons (in the trophy weapons section) to get an idea of the best route to take with world & character tendency, you can get platinum on the 4th play through (if it's too much of a grind you can use the glitch to dupe demon's souls) but i didn't read up on anything so made loads of mistakes and i took me 6 to get it