Typically they do nothing at all most of the time, what you want from a card is one that has great odds of winning the game but that also does something significant when it doesn't win the game
However, in a proliferate deck, you can be a threat to people running superfriends decks because you can remove loyalty counters using Spinal Parasite
Blue, Loyal Raptor Compy Swarm Ellie and Alan, Paleontologists Grim Giganotosaurus Henry Wu, InGen Geneticist Ian Malcolm, Chaotician Indominus Rex, Alpha Indoraptor, the Perfect Hybrid Owen Grady, Raptor Trainer Permission Denied Ravenous Tyrannosaurus Swooping Pteranodon Dino DNA Plains Plains Island Island Swamp Swamp Mountain Mountain Forest Forest Command Tower Command Tower
Certain Pokmon appear more frequently during different seasons, and players can only access some areas during a specific season