Getting this achievement requires at least two complete playthroughs, and a third whereupon you have to reach the giant blacksmith in Anor Londo.
The following is a list of equipment requiring boss souls. You need to upgrade a weapon to +10. This must be done with Andre, the Undead Parish blacksmith, he is the only blacksmith who can ascend ("Modify Equipment" in the blacksmith menu) weapons to +6. After +10, go to the giant blacksmith in Anor Londo and he can ascend them with the respective boss souls using the weapons listed under each one.
Soul of Sif:
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Dagger, Parrying Dagger, Bandit's Knife, Shortsword, Longsword, Bastard Sword, Balder Side Sword, Sunlight Straight Sword, Barbed Straight Sword, Dark Sword, Greatsword, Zweihander, Flamberge, Man-serpant Greatsword, Demon Great Machete, Claymore, Bastard Sword.
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("True" version, although they are both identically named in game they count as seperate weapons and have different stats and colouring.)
Broken Straight Sword, Straight Sword Hilt.
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Any shield that can be reinforced/ascended to +10.
Soul of the Moonlight Butterfly:
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Mail Breaker, Estoc, Rapier, Ricard's Rapier, Spear, Winged Spear, Partizan, Pike.
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Any shield that can be reinforced/ascended into +10
Soul of Quelaag:
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Scimitar, Falchion, Shotel, Painting Guardian Sword, Murakumo, Server.
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Uchigatana, Iaito, Washing Pole.
Core of an Iron Golem:
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Battle Axe, Butcher Knife, Crescent Axe, Gargoyle Tail Axe, Hand Axe.
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Caestus, Claw
Soul of Priscilla:
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Great Scythe, Whip, Notched Whip, Halberd, Lucerne, Scythe, Gargoyle's Halberd.
Soul of Ornstein (Must kill Smough first):
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Mail Breaker, Estoc, Rapier, Ricard's Rapier, Spear, Winged Spear, Partizan, Pike.
Soul of Smough (Must kill Ornstein first - this means at least two playthroughs for both of their souls!):
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Blacksmith Giant Hammer, Hammer of Vamos, Blacksmith Hammer, Club, Reinforced Club, Mace, Morning Star, Great Club, Large Club.
Soul of Gwyndolin:
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Shortbow, Longbow, Composite Bow, Black Bow of Pharis
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Sorcerer's Catalyst, Beatrice's Catalyst, Tin Banishment Catalyst, Logan's Catalyst, Oolacile Ivory Catalyst.
Soul of Gwyn, Lord of Cinder:
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Dagger, Parrying Dagger, Bandit's Knife, Shortsword, Longsword, Bastard Sword, Balder Side Sword, Sunlight Straight Sword, Barbed Straight Sword, Dark Sword, Greatsword, Zweihander, Flamberge, Man-serpant Greatsword, Demon Great Machete, Claymore, Bastard Sword.
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The following list requires tails to be cut off of the respective bosses. These are a one time chance (the exception being the gargoyles, two more will appear at Anor Londo but they do not respawn) so make sure you cut the tail off before you kill the boss! If you find the boss is about to die quit and reload your game.
Hellkite Drake:
- Drake Sword
Gaping Dragon:
- Dragon King Greataxe
Everlasting Dragon:
- Dragon Greatsword
Crossbreed Priscilla:
- Priscilla's Dagger (Attack her tail first! She gives you a free hit, cast Great Chaos Fireball on it if you use pyromancy - it will most likely come off straight away if you do)
Seath the Scaleless:
- Moonlight Greatsword (a useful tip is to run to Seath's crystal and wait for him to ready his attack and get out of the way. He'll break his own crystal and be stunned for a long time.)
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The following weapons are obtained from joining the respective covenants.
Gravelord Servant:
- Gravelord Sword
Darkwraith:
- Dark Hand
As of patch 1.05, Dark Wraith enemies in the New Londo Ruins also have a chance of dropping the Dark Hand.
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The rest of these weapons are obtained from enemy, phantom and boss drops.
- Black Knight Sword
- Black Knight Greatsword
- Black Knight Greataxe
- Black Knight Halberd
- Black Knight Shield
All Black Knight weapons are dropped from their respective Black Knights. If you miss any, there are respawnable ones in the Kiln of the First Flame
- Channeler's Trident
Dropped by the Six-Eyed Channelers. Non-respawning ones appear in the second floor of the undead church and the depths. There are 3 respawning ones in the Duke's Archives.
- Crescent Axe
Sold by Patches for 10,000 souls but can also be dropped by Patches upon killing him.
- Crest Shield
Dropped by Knight of Astora, Oscar upon your return to the Northern Undead Asylum. Encounter him in the same place as you did last time (he is the knight that gave you the Estus Flask).
- Silver Knight Straight Sword
- Silver Knight Spear
- Silver Knight Shield
Just like Black Knights, the weapons drop from their respective Silver Knights. They all respawn in Anor Londo.
- Stone Greatsword
- Stone Greatshield
Dropped by the Stone Guardians in the Darkroot Garden. Stone Greatsword can also be bought from Shiva of the East.
- Giant's Halberd
- Giant Shield
Bought from the Giant Blacksmith or dropped by the giant sentinel enemies in Anor Londo.
- Grant
- Sanctus
This weapon and shield are dropped by Paladin Leeroy, an NPC phantom invader in the Tomb of the Giants. He appears outside the entrance of Nito's cave, where you can see Ash Lake (Big hole showing a lake and giant archtrees). You must be human. Try not to let him fall off the cliff and lure him into the cave a bit where the crystal lizard is.
- Astora's Straight Sword
Picked up in the Valley of the Drakes, in front of the dragon corpse.
- Dragon Crest Shield
Same place as the Astora's Straight Sword.
- Dragonslayer Greatbow
Picked up in Anor Londo. On the upper floor of the cathedral (the large hall with the two Giant Knights and a Black Knight archer) there should be a broken section of the stained glass. Fall through and you'll end up in an area with a corpse containing the bow and some arrows.
- Dragon Tooth
- Havel's Greatshield
Found in chests in Anor Londo. Located behind an illusory wall disguised as a fireplace. The rest of Havel's gear can be found in the same room. Be careful, one of the chests is a Mimic.
- Bloodshield
Found on a corpse in the Painted World of Ariamis. On the bridge occupied by the undead dragon. You can either grab it and run back before the dragon reaches you, or kill it and grab the shield afterwards.
- Effigy Shield
Found in Tomb of the Giants. Located at the end of a narrow walkway, through an arch and guarded by a Black Knight. You'll be able to see it from afar. Be careful not to fall off the side!
- Black Iron Greatshield
Found in Anor Londo with the rest of the Black Iron set. In the huge room with the chandelier and entrance to the Painted World of Ariamis.
- Velka's Rapier
Found in the Painted World of Ariamis. After opening up the annex using the Annex Key, there is a shoddy looking barrier made of wood. Hit it with any weapon and it will break, leading to a corpse containing this weapon.
- Izalith Catalyst
Dropped by a pyromancer chaos witch in Lost Izalith. She appears right before the white fog leading to the boss. This is the same place that Kirk, Knight of Thorns will invade you.
- Demon's Catalyst
Dropped by the Demon Firesage in the Demon Ruins.
It is commonly cited that you need the Ghost Blade and the Jagged Ghost Blade dropped by the New Londo ghosts and Titanite Catch Pole for this achievement. You do NOT. The achievement will unlock with these weapons absent from your inventory.
Credit to gamertags Xelliz1, Illuminatus V, SEEGAAAA, Valeefor, Caxton8, MOPHREAK and FlaminG FrosT for polishing/correcting this list a bit.
