http://www.wowwiki.com/Talisman_of_Binding_Shard
This was the FIRST ever legendary item to drop in World of Warcraft from Baron Geddon in Molten Core, and was in fact a mistake, soon hot fixed by the developers upon the first drop; however, the player it dropped for was actually able to keep the item.
Would it be possible and/or plausible to make this item ingame and have it actually only have the 1 time drop, and for the player it dropped for to keep it? I'm not saying it's necessarily a good idea, but you must admit it is a fancy idea as it did actually happen in the real servers of wow.