The Pokemon franchise has always used Grass, Fire, and Water starters, with the sole mainline exception of Pokemon Yellow. Even then, in Pokemon Yellow, players would be able to add Bulbasaur, Squirtle, and Charmander because of how special the starters are. This typing selection creates the perfect triangle, where fire beats grass, grass beats water, and water beats fire. There are other type triangles in the franchise, but not all are as neat and many may be overpowered for the early game.