Coming back after leaving during Generation I

Generation I ran on 15 types and one Special stat

Red and Green went on sale in Japan on 27 February 1996, and Red and Blue reached North America in September 1998. The games held 151 species and 15 types. Ghost moves had no effect on Psychic, which left Psychic with one real weakness, Bug, and few Bug moves worth using. One Special stat covered both special attack and special defense, so Alakazam and Mewtwo hit hard and took special hits well at the same time. Critical hit chance came from base Speed. There were no held items, no breeding and no abilities. TMs broke after one use, and Kadabra, Machoke, Graveler and Haunter evolved only by trade. If your memory of battles is Psychic types sweeping everything, the rules explain it.

Three rule changes since 1999 reshape every battle

First, Gold and Silver split Special into Special Attack and Special Defense, added the Dark and Steel types and made Ghost 2 times effective against Psychic. Second, Diamond and Pearl in 2006 gave every damaging move its own physical or special category: Fire Punch became physical and Shadow Ball special, where before the move's type decided. Third, X and Y in 2013 added Fairy as the 18th type, retyped Clefairy as pure Fairy and made Dragon moves useless against it. A fourth change sits between them: Ruby and Sapphire added abilities, natures and the modern IV and EV system in 2002. Each has its own what-changed page with the before and after numbers.

FireRed and LeafGreen are the closest Kanto game on current hardware

FireRed and LeafGreen remade Red and Green in 2004 on the Game Boy Advance. The map, gyms and story follow the original, with Generation III rules underneath: abilities, natures, Special Attack and Special Defense, and the Sevii Islands after the League. Nintendo released FireRed and LeafGreen on Switch on 27 February 2026 as separate eShop downloads, with trades over local wireless and no online play, and HOME added them on 6 October 2026 as a one-way route in. Let's Go, Pikachu and Let's Go, Eevee (2018) are the other Kanto option: the 151 species plus Alolan forms, catching by motion instead of wild battles, and a second player on the same console. Choose FireRed or LeafGreen for the old structure, Let's Go for a shorter, easier lap of the same map.

Game Boy cartridges keep their saves only while the battery lasts

Red, Blue and Yellow store the save in memory kept alive by a small coin battery inside the cartridge. Many of those batteries are now past 25 years old. A dead battery loses the save, and replacing it erases the save too unless it is copied off first with a cartridge reader. A working cartridge still trades and battles over a link cable, and the Time Capsule in Gold, Silver and Crystal still accepts Generation I Pokémon. Pokémon Stadium on the Nintendo 64 reads cartridge teams through the Transfer Pak. None of this reaches HOME. The only Generation I route to HOME runs through the 3DS Virtual Console releases of 27 February 2016, Poké Transporter and Pokémon Bank. The 3DS eShop stopped selling software on 27 March 2023, new downloads of Bank and Transporter ended in March 2023, and Bank closes on 25 February 2027.

Limit. Copy the save off a Game Boy cartridge before a battery swap; the swap itself wipes it.

Plan the first week back around one game and one save

Day one: pick FireRed or LeafGreen on Switch, Let's Go, or a modern game such as Scarlet and Violet, using the decision table on the which-game page. Day two and three: play to the second gym or its equivalent and note which rules feel wrong; the what-changed pages for Generations II, IV and VI explain most of them. Day four: check your cartridges. Note which still hold a save, and leave any battery work until the save is backed up. Day five: if you own the 3DS Virtual Console versions and the 3DS already has Bank and Transporter, finish any move before Bank closes on 25 February 2027. Day seven: build a first team with the first-team guide instead of a 1998 roster.