It is card 13 of the 132 in the official Gym Challenge checklist. If you are completing the set, mark it in your collection to keep track.
Rarity: Holo Rare. The symbol in the bottom corner confirms it at a glance, as explained in Pokémon card rarities explained.
It exists in several finishes (Holo, 1st edition). Each one has its own price; the average above is for the regular version.
Artwork by Ken Sugimori. Some collectors chase every card by the same artist: how to start (in Spanish).
Abilities
Rebellion Pokemon Power
Whenever Misty's Gyarados attacks, flip 2 coins. If both of them are tails, that attack does nothing. Instead, shuffle Misty's Gyarados and all cards attached to it into your deck. (This power works even if Misty's Gyarados is Confused.)