What are all the differences between FRLG and RBY?

Question

This Christmas I got a legitimate GBA cartridge of LeafGreen. I want to know what all the differences are.

Comments

Congratulations! LeafGreen is an excellent game.

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Some differences can be found on this site: https://pokemondb.net/firered-leafgreen  https://pokemondb.net/red-blue https://pokemondb.net/yellow

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I'm still hoping Lt. Surge's gym isn't as difficult as it was in RBY.

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FRLG are the sequels to RBY.

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Generation 3 was a "resetting" of the series, so the differences would probably take a few hours and a few dozen answers to list.

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For now, i'll allow Links as answers.

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Held items were added, abilities were added, natures were added, EVs and IVs work differently (most notably that EVs are limited to 508 across all stats), soundtracks were changed, a female player character was added, a bunch of moves were added, a bunch of items were added, Generation 2 and 3 Pokemon were added, most glitches were fixed, a bunch of new glitches were added, there are two special stats, genders were added, a bunch of battle mechanics were changed, a bunch of NPC quotes were changed, a bunch of wild Pokemon encounter tables were changed, a bunch of NPCs' Pokemon teams were changed, a bunch of item locations were changed, breeding and eggs were added, move reminders and move deleters were added, a bunch of TMs were changed, move tutors were added, Cerulean Cave is accessible only after the Sevii Islands quest, the HMs for rock smash and waterfall were added, Pokemon summaries became more complex, shiny Pokemon were added, menu sprites were added, it's compatible with GBAs and some DSs but not GBs or 3DSs, the PC system was changed, Pokerus was added, friendship was added, NPCs' moves have PP, Pokemon trainers have names, key items can be used by pressing select, controls are explained at the beginning of the game, a bunch of multiplayer features were added, and probably a lot more changes.
https://bulbapedia.bulbagarden.net/wiki/Pok%C3%A9mon_FireRed_and_LeafGreen_Versions
https://bulbapedia.bulbagarden.net/wiki/Generation_III
https://bulbapedia.bulbagarden.net/wiki/Generation_II
http://www.smogon.com/forums/threads/mechanical-differences-between-the-gens.3474872/

Answer 1

Graphics are significantly better, everything is colourful and the dodgy sprites of Gen 1 are no longer.
17-type mechanics, Gen 3 game mechanics of things like EVs, IVs, natures, abilities, shiny/PKRS, separation of Sp. Atk and Sp. Def, reclassification of some moves like Bite, and retyping of Pokémon like Magnemite. No Mew glitch, no Missingno, more bag space. Sadly no time mechanics, so forget about using an Espeon or Umbreon. NPCs have names, and you can play as either male or female character. EXP share is a held item now. Limited number of Gen 2/3 Pokémon available, including added evolutions and pre-volutions. One of the Legendary Beasts available after postgame, (save your Masterball for this as it will disappear permanently if it flees using Roar.)
Elite 4 and Champion can be rematched at higher level. Their teams also make use of newer Pokémon.
Some trainers can be battled again using the VS seeker.
2 Day Care facilities. The one in the Sevii Islands can take 2 Pokémon and allows for breeding.
Some moves function differently, for example binding moves no longer restrict use of attacks, and Venusaur can no longer exploit the Toxic & Leech Seed glitch.

Sevii Islands - accessed after badge 7, and also added postgame featuring Team Rocket. New functions including a move reminder found here. This is also a decent spot for grinding levels by constantly rechallenging trainers, and the new home of Moltres.

I'll add if I think of anything more.

Comments

Who's the roaming legendary?

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This answer is definitely not complete.

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Entei, Raikou, or Suicune roams mainland Kanto after completing the Sevii postgame. Which one is available is determined by your starter. Bulbasaur >> Entei, Squirtle >> Raikou, Charmander >> Suicune.

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Darn it. I wanted Raikou. But okay.