Pokemon gold stars are the card versions of shiny Pokemon. On gold star cards at the end of each card name there will be a gold star; hence the name gold star cards. There are 27 star cards. The star cards are only made of specific Pokemon. The gold stars are of Kyogre, Alakazam, Mewtwo, Mew, Espeon, Entei, Suicune, Regirock, Regice, Registeel, Charizard, Umbreon, Raikou, Metagross, Rayquaza, Celebi, Groudon, Jolteon, Flareon, Latias, Latios, Gyarados, Vaporeon, Torchic, Mudkip, and Treeko.
Completing the gold star set is like completing any other TCG set but much more difficult. There is very few people who have completed this set. The gold star Pokemon are just shiny Pokemon converted into cards. Like shiny Pokemon the coloration of the Pokemon is different. There might be a big difference or sometimes you can barely notice the difference. Like Rayquaza gold star the coloration of the Rayquaza is black instead of green. Gold stars are extremely hard to get. They are only available in some sets. Like Pikachu star in Holon Phantoms, or Mew and Charizard star in EX Dragon Frontiers, or Celebi and Alakazam in Ex Crystal Guardians.
Some gold star cards are very famous, for example everybody wants Charizard gold star. Charizard gold star is very rare and is probably the most famous gold star card out there. The value of a mint condition Charizard gold star is from eighty to one hundred and twenty dollars maximum. However its not the most expensive gold star card, the most expensive star cards would be Umbreon star or Espeon star; as they are even harder to pull than any other. Umbreon and Espeon star are only available in the POP 5 set. They are not available in holographic unless you get the players promo one in Japan which is worth very much, most up to two thousand dollars for Umbreon star holographic.
The next most famous star card would be either Pikachu star or Rayquaza star. If you have great luck you might even pull a star in a store bought pack but it is highly unlikely. They say gold star cards only come in one of three booster boxes. But some people have great luck pulling stars in packs. Good luck with your gold stars!