1. No Rarity Symbol Pikachu Illustrator (1997): This is generally considered the most valuable and sought-after Pokémon card. It was given as a prize to winners of a Japanese illustration contest and only 39 are known to exist.
2. "No Rarity Symbol" Promotional Cards (1997): These cards, including the "No Rarity Symbol" Pikachu, were given away in promotional campaigns in Japan. They are extremely rare and highly sought after.
3. Gold Star Pokémon (2004-2008): These cards were introduced in the EX series and are notable for their gold star symbol. The rarest ones, like Gold Star Espeon, are highly valuable.
4. Holofoil Trainer Number Cards (1999-2003): These cards are numbered and have a unique holographic pattern. The rarest ones, like Trainer Number 4, are highly sought after by collectors.
5. Japanese "First Edition" Shadowless Cards (1999): These cards are identifiable by the lack of shadow behind the Pokémon artwork and are extremely valuable, especially in near-mint condition.
Factors Affecting Rarity and Value:
* Production Quantity: The number of cards produced is a major factor.
* Distribution: The way the cards were distributed (e.g., contest prizes, promotional events) affects their availability.
* Condition: A card's condition significantly affects its value. A pristine card will be worth much more than a damaged one.
* Popularity: The popularity of the Pokémon featured on the card also influences its value.
So, there's no single "rarest" card. It depends on what you consider rare and valuable. But the Pikachu Illustrator and other "No Rarity Symbol" promotional cards are generally considered the most sought-after and expensive Pokémon cards.