I have an idea about Shazellim regarding something that bothered me.
The description says that the Red Wizards made it to slay Harpers. The item is given the ability to instantly kill, the most powerful ability a weapon with Purpose could have in 2E. Pehaps to limit this, Shazellim's Purpose is to slay Bards, a pretty small group. Now, while Bards may be the most common class amongst the Harpers, they are certainly not the only class, nor necessarily even the bulk of the organization (look at Elminster, Khelban, 7 sisters, etc., heck, even Khalid and Jaheira).
In any case, as far as BG2 goes, ARE there any Bard opponents in the game? The only Bard you can pick up is Haer'dalis, and he's from another plane. What's more, even if there are Bards, there's no sign or clue letting you know when you're gonna meet one. Some of the Harpers you deal with might be Bards, but there's no way for the gamer to tell, and thus whatever "coolness" the blade might have are lost.
What I propose, if it's possible, is to make the sword much more useful in all the Harper battles by having it's ability work against any Harper, not just Bards. This would help explain why everyone's so quick to blame Jaheira and call her evil (nobody else in your party is going to wield a scimitar, are they?).
I don't know anything about programming, so I don't know if you can just attach a flag of some sort to all the Harper characters and let the sword work against them. If not, I thought you could tie the flag to an item, and what better item than the Harper necklace that Jaheira wonders at. This way, whenever an npc is killed and they have a necklace in their items, then the gamer knows that they were a Harper and thus vulnerable to Shazellim.
I thought that it would make the blade more useful, give lots of room for extra dialogue all over the place, explain the animosity towards Jaheira from later Harpers, and actually let Jaheira kill something for once ("yay, my kill score went up from 0 to 4!")
It's supposed to be an anti-harper blade, so it would be useful in all the harper battles, but can be replaced later since it's otherwise only a +1 weapon.