The Ancient Mew card is truly unique among Pokémon cards. It has a completely different front and back design, both sides are holographic, and all the text of all versions of the card is written in English transcribed into Futhark runes (excluding the copyright information). Because of the stylization of the card, particularly the hard-to-read text and highly distinctive backside, Ancient Mew has never been playable at tournaments (even in unlimited format). Also noteworthy is the fact that the original artist is uncredited, again most likely due to the card's stylization.
The Ancient Mew Card was originally made as a Japanese promotional card for the Revelation Lugia movie, and was released in July 1999. The card wasn't merely handed out, but came in a promotional booklet with a clear sleeve designed so that the card appears to act as part of the artwork, with a drop shadow and everything.
The Ancient Mew Card actually appears in the movie itself. It is the first element of the Pokémon collection belonging to Gelardan (dub name Lawrence III), and the only thing he has left by the end. Perhaps the movie's creators hoped that you would treat the Ancient Mew card as the first element of your obsessive Pokémon collection as well. Gotta catch 'em all!
As a side note, the initial printing of the Japanese card had a typo in the copyright information, with Nintendo misspelled as "Nintedo". There was another printing of Japanese Ancient Mew cards, completely identical to the first run, but with the mistake corrected. There are actually fewer of the corrected Japanese cards than those with the error, counter-intuitively making the corrected Japanese cards rarer and potentially more valuable than the cards with the mistake (but not to be confused with the English cards that were all typo-free; you can apparently tell the English cards apart from the Japanese cards based on the holographic speckles, but, uh, I can't really see the difference in the pictures online).
Anyway, the English version of the Ancient Mew card was similarly released to coincide with the release of the English dub of the same movie, Pokémon the Movie 2000: The Power of One, in July 2000. This Ancient Mew card did not come in a fancy booklet like in Japan, but was simply handed out at the box office in just a cellophane wrapper. At least all non-Japanese releases of the Ancient Mew card came with a teaser card in the respective country's language (if you have one in a language other than English, would you please send me pictures?). There were Wizards of the Coast events where translation cheat-sheets were provided (can anyone send me a picture of this as well?). According to these cheat-sheets, the symbols behind Mew stand for "Birth", "Enthronement", "Right of Succession", and "Death", and the text of the card translates as:
I remember when I first heard about Ancient Mew when the card was new. My first thought was of the ancient carving of Mew shown in Mewtwo Strikes Back, which was created by the native people living in the Amazon jungle to honor their protector god and enshrine its eyelash. The design of the Ancient Mew card is similar to this carving, but, I feel, has a different spirit, as if it were created by a different culture than that of the Amazonian natives. First of all, the runes on the card are Germanic, implying a European rather than South American origin. Next, the Mew in the carving appears more stern and threatening than the more playful Mew of the Amazonian carving. The deciphered writing on the card is certainly ominous, questioning whether Mew is benevolent or malevolent, and the symbols surrounding Mew seem related to monarchy. This clashes with the South American natives' view of Mew as a protector that should be offered thanksgiving. I would guess the ancient Europeans saw Mew as powerful and less than benevolent, and perhaps as a symbol of a king or the divine right to rule.
One of the motifs found on the Ancient Mew card also appears on the Japanese cover of Neo Premium File 2. The cover of the folder depicts a carving of a Xatu totem, surrounded by carvings of the legendary birds, Unown, Kabutops, Smeargle, and other Pokémon (the back cover is also pretty cool). On the Xatu totem are triangular designs that are strikingly similar to the triangles displaying the weaknesses and resistances of Ancient Mew. The Xatu totem is also surrounded by element circles, much like the back design of the Ancient Mew card. The recurrence of these motifs suggest that Ancient Mew might be related to the Ruins of Alph. Perhaps it was the same culture that built these ruins that created the Ancient Mew design?
Also, that triangle with the eye in it seems kinda familiar...
Perhaps the Psychic All Seeing Eye is a clue on the Ancient Mew card signifying that there is a map on the back of the United States Declaration of Independence, a map that will lead us to the greatest treasure of all time, safely guarded by the Freemasons through the ages... Those who are pure of heart may follow the clues and reach the goal: a truck with a Pokéball underneath containing Mew! It all makes sense!