There are 1,025 Pokémon so far, though that number is sure to increase when the tenth generation arrives. You also have an additional 59 regional forms, 48 mega evolutions, 32gigantamax Pokémon, and multiple Pokémon that naturally have different forms, such as the Unown forms that spell the...
However, the difference in these teams is the usage of well placed offensive pokes as the team's trump card. For example, in JabbaTheGriffin's recent team, he uses a Scarf Jirachi to revenge kill threats that would otherwise be trouble (mainly Mence that will forever trouble stall teams)...
Kanto/Gen I: Magnemite, Pikachu, Charizard, Eevee, Bulbasaur Johto/Gen II: Umbreon, Marill, Wobbuffet, Azumarill, Pichu Hoenn/Gen III: Sableye, Flygon, Whismur, Jirachi, Spheal Sinnoh/Gen IV: Piplup, Empoleon, Luxray, Glaceon, Lucario Unova/Gen V: Cinccino, Snivy, Swadloon, Oshawott, Chan...