As far as I know the rarest card in existence is Prerelease Raichu.
To my knowledge there are only 4 currently in existence, and most people deny they even exist.
I cant ever deny those were ever made now, but I would really question if WOTC or PUI would authenticate em as being real. Kinda like money and coins being legal tender and all. But I mean has any of us seen a pre-release raichu?
The ones in the Japanese Catalogue (back in 1999 I believe...)
The trophy Pikachu Gold, Silver, Bronze (3 copies in the world)
The Zapdos, Moltres, Articuno of Phone card size (3 copies in the world)
The illustrated Pikachu (the one Pikachu holding a pen drawing, 2 copies in world or something?)
The Mew with a logo on the right (Mever seen anywhere! even ebay)
The executator special ones (Never seen anywhere! even ebay)
The snap prize card (veries cards only 1 copy in the world)
The university Magikarp (? Copies)
The Tropical wind (2 Japanese versions, ? copies in the world)
Victory Ring
Victory Energy
Tropical Wind is kinda more common though, I think a good 10 of em exist worldwide could be slightly less. the Illustrator card (had a rare chance to own one few years back) I think has about a good 100 copies world wide, the story behind illustrator Pikachu ties in with the Vending Sheets they had, I believe most of the vending cards if not all were all part of a contest, artist would draw the pokemon and the winners would recieve the illustrator card and have their picture put on a pokemon cards, yet the illustrator may seem to be the rarest one out of all thats listed, but it aint. I think though the Gold Pikachu Trophy might actually be the rarest, but theirs disputes about it on all of it though.
But going back I got this card some time ago, it appears to be a Vending Series Mewtwo but different, Japanese now of course, with symbols on its body and all and wirting at the bottom of the card, its actually the same picture and all but totally different from the vending series card itself, anyone got any info on this? I havent really seen many of those in existence either, not even on ebay.
I have put the cards I was talking about in following link:
www.smason108.co.uk