I suggest adding the mechanics of critical capture in the game.
Since Generation V, when a Poké Ball is thrown, a special type of capture that is much more likely to catch a Pokémon, called a critical capture (Japanese: 捕獲クリティカル critical capture), may occur. When a critical capture occurs, the Poké Ball will make a high-pitched whistling sound as it is thrown, then pause in mid-air, and shudder before it drops down to the ground, shaking only once on the ground before the Pokémon escapes or is caught.The probability of a critical capture occurring depends of the number of Pokémon that have been caught in the Pokédex.
I think this mechanism can enhance the fun of the game.