How many agent mew cards are there?

There is only one Agent Mew card.

While there are different versions of the card (such as the Japanese version or different printings), they all represent the same card: Agent Mew.

It's important to note that "Agent Mew" is a specific card, not a set of cards. It's a rare card from the Japanese "The Origin of Species" set, known for its unique illustration and powerful effect.