These cards are identified by a black star symbol with the word PROMO written across it, hence why theyre also called Black Star Promos. The demand for these cards varies, mostly depending on how difficult the Promo was to obtain or how popular the featured Pokmon is

They look as follows (the dagger marks signifying the fact that it is impossible to tell the beginning and end of the sequences): Nidoran m, Diglett, Abra, Fire Energy, Starmie, Ponyta, Fighting Energy, Koffing, Pikachu, Doduo, Fire Energy, Gust of Wind, Machop, Lightning Energy, Gastly, Ponyta, Tangela, Grass Energy, Squirtle, Voltorb, Psychic Energy, Sandshrew, Weedle, Rattata, Water Energy, Drowzee, Poliwag, Fighting Energy, Charmander, Potion, Onix, Lightning Energy, Koffing, Magnemite, Psychic Energy, Pidgey, Abra, Metapod, Water Energy, Diglett, Staryu, Fighting Energy, Caterpie, Switch, Vulpix, Fire Energy, Voltorb, Machop, Grass Energy, Poliwag, Nidoran m, Rattata, Lightning Energy, Gastly, Doduo, Psychic Energy, Tangela, Sandshrew, Bill, Fighting Energy, Vulpix, Squirtle, Fire Energy, Pikachu, Bulbasaur, Drowzee, Grass Energy, Onix, Pidgey, Lightning Energy, Staryu, Charmander, Metapod, Psychic Energy, Energy Removal, Magnemite, Water Energy Poliwhirl, Maintenance, Farfetchd, Ivysaur, Pokmon Center, Machoke, Jynx, Full Heal, Kakuna, Double Colorless Energy, Porygon, Charmeleon, Maintenance, Poliwhirl, Raticate, Pokdex, Nidorino, Magikarp, Professor Oak, Magmar, Pokmon Flute, Porygon, Haunter, Energy Retrieval, Seel, Dratini, Double Colorless Energy, Growlithe, Wartortle, Full Heal, Dewgong, Defender, Kakuna, Magmar, Pokmon Center, Raticate, Seel, Revive, Nidorino, Kadabra, PlusPower, Dewgong, Super Potion, Arcanine The length of the sequences (77 and 44) which add up to 121 cards are too much of a coincidence to assume anything other than that they were printed on one single sheet and then separated before being inserted into packs

I firmly believe that given the soapbox that Sheldon and the other members of the Rules Committee have an article extolling the virtues of playing with un-set cards and a sincere personal recommendation to try it would have been enough
Even if those weren't a problem, there wasn't a serious chase card in the set or popular Pokmon like Pikachu or Charizard