In this game you are a 10-year-old boy, now old enough to receive your first Pokémon. You train this Pokémon by using it to battle with other Pokémon. Your main objective is to collect 8 gym badges to face the Elite Four and Pokémon League Champion of Kanto. You do this by defeating each gym leader in a Pokémon battle.
There are two parts in gameplay to this game. The first is your main character. You walk from place to place, goes up to talk to people, and find items. The second part of the gameplay happens when another Trainer has seen you, or you come across a wild Pokémon.
In the Pokémon battle, you can select from four options: Attack, Pokémon, Item, and Run. In the attack option, you choose from the Pokémon's attacks to use on the opponents Pokémon. This either drains their HP (lowering a Pokémon's HP to zero will knock them out), inflicts a status condition (like sleeping or poison), or changes stats (attack power, speed, etc). In the Pokémon option you can switch the active Pokémon in battle. In the item option you can either use items on your Pokémon (to heal them), or in a wild Pokémon battle you can throw a Poké Ball to catch them. The run option is only available in battles with wild Pokémon, you cannot run from a Trainer. The battle ends when one Trainer has no remaining Pokémon.
Your rival is always one step ahead of you, and challenging you to battles. You will run into the Rocket Gang, a group of criminals who use Pokémon for evil purposes. You must defeat many of their grunts and their leader in order to foil their evil schemes.
You can also link up to Pocket Monster Akai in order to trade Pokémon or battle with your friends. This is necessary to get all 150 Pokémon, because not all of them appear in Midori.
There is an early sketch for the first two Pokémon games, which shows three characters with the Kanto region's starter Pokémon: the protagonist with a Bulbasaur, his rival with a Charmander, and an unused female trainer with a Squirtle. The last of these three trainers was most likely intended as a playable character, and it is also possible that depending on who you chose to play as, she would act as a friendly "pseudo-rival" to the player, much like Brendan and May from Ruby and Sapphire as well as Lucas and Dawn from Diamond and Pearl. However, possibly due to technical limitations of the original Game Boy, she was not implemented into the final version of Pokémon Red and Green. The Game Boy Advance remakes of the first two Pokémon games allow players to select their gender.
Virtual Console Alterations
Pocket Monsters Midori and its counterpart versions were rereleased for the 3DS Virtual Console to celebrate the Pokémon franchise's 20th anniversary in 2016. Since the Nintendo 3DS isn't compatible with the long-obsolete Game Link Cable, these releases use the system's local wireless features for link trades and battles. Additionally, several attack animations have been toned down for the safety of players with photosensitive epilepsy or other sensory conditions.