Staff of the Magi is cheat-generated. The other two are two of the Legendary Artifacts of the game, which you need to find pieces of and get Cromwell (the dwarf in Docks district) to forge them into a real weapon. If you go to play BG2 Online at Mplayer.com, look for a game called "Mists of Shadow." I can give you all three of the artifacts then
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On the heights, all paths are paved with daggers.