[ed. note] I found this on the Mystara Mailing List. It's in the grand old tradition of Powerful Swords of Blackmoor, started by Arneson himself in '72.
+3 two-handed sword, +5 vs. orcs, undead, and dragons
Powers:
Extraordinary Power: The user of the white avenger may inflict four times the normal damage on each hit. This power lasts for 1 to 10 rounds when commanded, up to three times per day.
Languages: Arbus can speak (and read) goblin, hobgoblin, orcish, gold dragon, common, and magic.
Intelligence: 12 Ego: 6 (Will Power: 19)
History: Arbus was forged in Blackmoor to serve as a companion blade to the famous White Sword. Unfortunately, it was stolen before it was ever used in Blackmoor by agents of the Empire of Thonia. It was subsequently turned over to a Thonian paladin by a devious emperor with none the wiser to its abduction. The White Avenger obtained its nickname in those days as the great paladin - Sir Galladon of Etheria - used it to smite the hordes of chaos throughout the land. Sir Galladon finally met his match, however, on a trip to the elemental plane of water - where he was defeated by an ambush of several crab-like ice creatures known as hydraxes. The leader hydrax took the blade, and kept it for several hundred years...
Followup note by Zimriel:
Of course, I do not recognize that Thonia-Blackmoor's future is bound up with Mystara's. That makes the sword's future uncertain; accordingly I have cut that from the History section.
If the above be true, then the sword was crafted long before the kingdom's war of independence. It must have been stolen before the darkspawn of the Egg of Coot invaded during the so-called "five victories", probably by the Iron Duke's agents at a time when he was more loyal to Mohacs.
Iyx was not a devious Emperor. He was a spoilt child and remained so until the long-awaited day he was poisoned (unless he really did die of gluttony). His successor seems to have been more politically skilled; he certainly had the presence of mind to give the Iron Duke a task to carry out (retaking Blackmoor) and insufficient resources either to perform it properly or to do anything else.
It would appear that Sir Galladon holds the sword now, both lawful and good tools of a corrupt and near-evil empire. If "Etheria" even exists on this plane (compare "ethereal") it is probably a subprovince of Thonia off the DA3-4 maps.
Technically, Arbus is not stolen. It was taken from a compromised church in a rebel province, and returned to the church in a loyal province. Morally, however, Arbus was taken from the place it was made to defend. And, justified or not, this was also an intrusion by the state into the church's affairs. It would be interesting to see how the sword informs him of this. If it doesn't, is it that the sword hasn't the self-confidence (ego)? or is it that the true cause of law and good does not rest in an independent kingdom of Blackmoor...
One thing Blackmoorians and Mystarans agree on - it's probably not the latter. If the former, there are two adventure hooks I can see. Both are based on the sword's Greek-tragedy fate.
One obvious idea is to have the PC's meet up with Galladon when he's debating on taking on an evil force in the Plane of Water. Give your party the legend / premonition first. The party will know that the paladin won't return. Maybe Galladon knows too, deep down. The paladin needs to decide whether or not he'll go through with it anyway. This is especially recommended for the Mystara-based. Will the party try to avert the paladin's fate? or will the party seek to avert the temporal paradox?
If your party is Blackmoor-native, then the sword could be in the Plane of Water. In this case, the sword's ego of 6 is not natural. It went down because the sword realized it had erred; it hadn't told the paladin to return it to the North. In this case, the sword's functionality is defective. It loses bonuses and special abilities. It might even break.
Any thoughts? e-mail me :^) zimriel@sbcglobal.net