I have come close to falling on an NPC from on top of the Nexus, but not hit any. What I have done is walked off the short ledge right next to the sitting Sage Freke, fell 1 foot, and stepped on his head :lol:. It counted as a hit so I immediately quit the game through the PS button.
Each time you connect to the Demon's Soul server your world tendencies are averaged to the global world tendency which is a composite of all the other games connected to the network. This is almost always one step below pure white so if you can connect online usually it is just a matter of killing one boss each level to get pure white.
The "proper" way to get pure white is to lower tendency to pure black, kill the primeval demon and the named black phantom of the level (Miralda, Scirvir, Rydell, Satsuki, Selen Vinland) WITHOUT existing to the Nexus, then kill one more boss to get to pure white. As long as you leave one boss alive in each level and you have not yet done the pure black world tendency events, it is possible to attain pure white. On the flipside, pure black can be obtained at any time as long as you have enough stones of E eyes.
If you launch Demon's Souls without signing out of PSN first when you have pure white world tendency in any of the levels, you risk them being downgraded to one step below pure white when your game is averaged against the server. So I wouldn't recommend doing that until you have completed all the white world tendency events for the level you currently have pure white.
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If you still have pure white in Boletaria palace, head on over to the Dragon's roost in 1-1 near the bridge the red dragon was covering. Both Dragons are gone and you can grab the items. If you have already grabbed all the gear in Miralda's Execution ground (including the armor at the base of the tower and the colorless demon soul on the beam in the middle of the tower) then that is all the white tendency events in Boletarian Palace. I would wait to do the black world tendency events until after you kill penetrator as the primeval demon spawns pretty close to his archstone if you backtrack and it is much easier to backtrack to the Executioner Grounds when all the shortcuts are open.
For Stonefang go for black tendency after you clear out all the tunnels of treasure on the way to flamelurker. What I did was start at the Armored Spider Archstone, fall down to Scirvir, killed him, then jumped to my death to spawn back at the spider archstone (you will forfeit the souls you were carrying). Then I backtracked to ledge above Ed's shop, rode the elevator down to the start of the level, and killed the primeval demon. Finally use flamelurker as the final bump to pure white so that you can grab the Dragon Bone Smasher before you fight Dragon God. Exit to the Nexus with the sword, kill yourself in the Nexus if still in body form, re-enter at Armor spider archstone and drop down to Scirvir to show him the sword, then drop down the rest of the way and kill Dragon God.
Latria I used Maneater as the bump to pure white after doing pure black events. Start in 3-1 to kill black phantom Rydell, and then proceed all the way down to the swamp to kill the primeval demon in 3-2.
Shrine of Storms I used Old Hero as the bump to pure white after doing pure black events. Procedure is much the same as Latria, start at 4-1 to kill Black Phantom Satsuki, then run the rest of the way to the start of 4-2 to kill the primeval demon.
Valley of Defilment, by this point I was fairly confident so I waited to use Saint Astrea as the final bump to pure white after doing pure black events. If in pure black you start at the dirty colossus archstone and back track the black phantom Giant Depraved one which spawns there will always drop a stone of EE when killed. If you have difficulty finding enough stones of EE to do the black tendency events in the other worlds this is a great place to farm them consistently.
Generally I did the pure black events before the second to last boss so in case I screw up somehow (like forgetting to change to soul form after obtaining pure white and then dying) I still have a backup boss to get the final push to pure white.
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4-1 is usually my first stop after I grab all the pure white gear in Boletarian palace once Phalanx is dead. The crescent falchion is a great low level weapon. Rather than fight the dual katana skeleton guarding it, I toss a soul remains to the side as it runs toward me to distract it, grab the weapon, then jump off the ledge to the ground below. 4-1 is also a great place to farm for souls. Parry and riposte with the crescent falchion to kill the skeletons in one hit and gain a bonus to soul collection. Clear the skeletons to the entrance of the fort, then backtrack, exit, and reenter several times for a quick boost to your soul level.