Actually, I created the Holy Avenger sword in NWN, and yes, no one can wield it, it's level will be 47. Well, depending on what dispell you use there, that is, Dispell or Greater Dispell. At least I tried to make it as exact as possible, had the desc open when creating it
As for weapon type, then Carsomyr +5 is no doubtedly a Greatsword. Simply in NWN the smaller races use bastard swords as 2H swords. Sure, Aribeth was an elf, and elves are marked as "medium" race, but in the game elves seem to use bastard swords as 2H ones.
For fun and giggles I created few BG2 weapons, and scattered them throughout the game, as loot from big mobs or additional quest rewards of harder quests. Most of BG2 weapons, even in NWN, had totally reasonable level requirements (lvl 13-20) and thus were quite useable. I simply didn't like how some weapons looked in NWN, and also missed some weapons, which became dear for me in BG2
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I didn't kill her to get her weapon. The thing I liked to do throughout the game was to disarm the opponent (Improved Disarm) and then beat the lights out of them with their own weapons. It's fun to disarm them, pick up their weapon and then go into Parry mode. Then, when they attack me and I Riposte, they get a taste of their own weapon. Eh, fun heheh.. But I am - at times - a reasonable person, and did not kill all the opponents. You can make deals sometimes
Was a funny fight, for example, with Meldanen. Sounds were like:
Meldanen attacks: *screams* Rrargh!
Me: Parry *clang*
Me: Riposte *smack!*
Meldanen: *screams* Oww!
Me: *Attack Of Opportunity* *smack!*
Meldanen: *screams* Owie!
Meldanen attacks: *screams* Aargh!
Me: Parry *clang*
Me: Riposte *smack!*
Meldanen: *screams* Ouch!
Quite a cacophony heheh.. Oh well, I love Parry.