OK, I'll get the ball rolling. This is rather long, so please bear with me.
See, I'm very much interested in the esoteric and divinatory aspects of the Tarot. Being able to brush back the veils of time to take a glimpse of what the future holds is for me a truly wondrous thing.
I dunno if some A.T.-ers from my country have heard of this. Anyway, in our province (our country has provinces like the U.S. has states, though we're not federal), there is a story about a scion from one of our most prominent families. Being rich, he was nothing but a dissipated dilettante, a bit like your trust fund babies. There's only one thing he was serious about, and that's magic and the occult. There have been many whispers about him, but since wealth can usually buy silence, none can really be verified. Not even the Catholic Church, which still held considerable influence during that time, can touch him.
As he delved deeper into the occult, a mishmash of western traditions and our very own animistic/shamanistic brand of Christianity, he slowly became unhinged. Some say that what he was learning was getting too abysmal and that these forbidden knowledge was never meant to be divulged to any but the most enlightened of men. Others say that he was slowly being possessed by a legion of demons. As he sank deeper and deeper even his family got scared of him. Whereas before they made excellent use of his divinatory gifts for their financial benefit, now they don't quite know what to do with him. They decided that they don't really care what's happening to him, and he can't be allowed to besmirch the family's reputation. So he was locked, along with his tomes and books and grimoires in his room, which was kept dark because he can't stand any light.
Before he expired, he sought to impart all of the knowledge he gleaned. He cut black squares from the voluminous drapes that shrouded his room. In it he inscribed symbols in red and brown, smearing these as he did with his blood and shit. Now these cards may not specifically follow the structure of the Tarot, it may just be an oracle so we don't really know. Anyway in his last week his room was unusually quiet, and the food they prepared for him lay untouched against his door.
So they called a close friend of his, another occultist who hasn't quite gone into the deep end. He came to his room to check if he's still alive. He was dead by then, so when the coast is clear his family swept his room to prepare for his funeral. His friend requested that his occult effects be turned over to him. The family of course wanted nothing to do with any of his stuff, so they agreed. Along the items his friend collected were the square pieces of cloth. These he immediately and personally crafted into a magnificent set of black, red, and gold cards before proceeding to study them.
At this point his fortunes began to rise. And as his wealth rose dizzyingly, his mental health plunged. People said he would always be seen with a lacquer box he guarded fiercely. The help would always see him in his study, looking at the cards and writing, writing, always writing. It seems that the cards held the absolute key to the future, and anything asked of it would be answered with a hundred percent accuracy. But as with everything, any great boon exacts payment in equal measure. One day he just disappeared, along with his box and the great red book he was writing on. None of his possessions have been touched, not even the valuables in his safe.
What happened next was open to conjecture. But the story people most believed was that he found a way to use the cards without having them turn on him. They say that when the cards get "hungry", he would find just the right person to whom he would "lend" the cards. These desperate souls would use it for their own purposes, delighting in all the gifts it bestows. At the most critical moment, the cards would turn on them, feeding on their mental essence until it leaves them a gibbering husk. In the end when the cards have been sated, they would always get their way back to their rightful owner. He would then use them for his purposes, kept safe in his riches, until the next time it grows hungry.
I guess the lesson one can glean from this is that one should be careful of strange decks. So treat your Rider Waite Smiths and Thoths and what-have-you's well. They're your friends, and you don't have to trade your brains to get them to help you. And beware of strangers bearing gifts in black, red, and gold.