First, I don't think any of my players read this board, but if you do don't read this thread.
Okay, so, I've been running a game for about a year or so. Back in November, I placed a simple, masterwork shortsword in a side-adventure. The PCs almost didn't take it, which would have been a pity. In the end, though, the exact character I'd hoped actually did grab it.
Since then, it has slowly been revealed to be an intelligent weapon that is cloaked to hide its magic aura. Its purpose is to aid wizards in accumulating as much power as posible. It's taught its bearer a couple of spells and given some advice, telepathically, as well as demonstrating a couple of pretty cool powers. On the other hand, it has also urged the bearer to keep its existence quiet.
So far, she has complied, even going so far as outright lying to the other PCs. Only the warlock has seen anything unusual and he's decided to let her play her hand. The wizard PC, and all the players, are bloody freaked by a sword wanting to remain secret. The wizard is willing to give it a go, though, since the sword said it'd like to see her as guildmaster. She has been leaving the sword in her inn room an aweful lot, though, so she can have secret conversations with various people.
Now, the bastardry (to be revealed in another couple levels): The sword is nothing special in any way, shape, or form, other than being masterworked. It is, instead, and item possesed by a glabrezu (as per BovD). Actually, that's not even true. The wizard willing lowered her resistance against the demon, which allowed it to slip into her body. The glabrezu has been doing little more than playing watcher and talking to the wizard, but started off giving aid to her. He is working to corrupt her, and has begun her downward trend. I'll be interested to see how far the PC takes this.
So, is that bastardy enough?