Generation III introduced a new attack specific to the Pikachu evolution line called Volt Tackle. In the Japanese version of the game, Volt Tackle is known as Volteccer.

Volteccer is the name of an attack used by Pulseman, the protagonist of a self-titled Sega Mega Drive game developed by Game Freak in 1994.

There is an unused battle theme for the three legendary beasts, suggesting they were planned to make a return after Gold, Silver and Crystal. The legendary beasts made a return in FireRed and LeafGreen, and could have been an implementation of the original idea to put them into Ruby and Sapphire. It's also possible the track was simply used for testing purposes.

Many sprites of the backs of Pokemon are actually minor edits of sprites from Gold, Silver and Crystal, with Farfetch'd, Caterpie, Weedle and Kakuna being almost identical to the previous sprites, simply having an extra shade or two of color and updated palettes.

In Pokémon Ruby and Sapphire, map data exists for a closed version of the Flower Shop (which in the final version is usually always open) on Route 104. In this unused map there is only one non-playable character, and they inform the player that the Flower Shop is closed.

The map was originally used in the Pokémon Festa 2002 demo to limit the player's experience of the game. It was later removed from gameplay in the final version, but still exists within the code.

Ruby and Sapphire were the first Pokemon games to introduce Abilities. These introduced new strategies for Pokemon battles. Some examples include Levitate, which makes the Pokemon immune to Ground moves, and Vital Spirit, which prevents sleep.

Junichi Masuda stated that while developing Pokémon Ruby and Sapphire, Game Freak considered changing the number of Pokémon the player can have in their party, and the number of moves a Pokémon could learn. The idea was later scrapped. It is currently unknown what sort of potential changes were to be made.

Two of the optional male names at the start of the game (one in Ruby and one in Sapphire) refer to "land" and "sea" respectively. In the English version, these are Landon and Sean; in the Japanese version, リクヤ Rikuya and カイト Kaito (陸 riku means land and 海 kai means sea). This is also the case in other languages.

When playing as a female, two other optional names are also available: Terra and Marina.

An unused sprite for a member of Team Aqua exists in the internal data and is identical to that of male Team Aqua Grunts with the exception of a mirrored body, modified coloration, the addition of a mustache, and a bandanna around the Grunt's left arm.

There are 2 unused abilities. No Ability and Cacophony.
No Ability is presumed to be an error handler, and is used when the game manages to find a Pokémon with an ability of ID set to 00. The term isn't used in the final game because all Pokémon were given abilities.
Cacophony is an ability similar to Soundproof, which isn't assigned any Pokémon in the game. It's assumed it was meant to be the ability for Whismur, Loudred, and Exploud, given their nature for noise-based attacks.

There's an unused sprite in Pokémon Ruby and Sapphire that appears to be a revamped (and stretched) sprite from Game Freak's first game, Mendel Palace.

In Ruby, Sapphire, and Emerald, there is a man in the Devon Corp. that speaks about entering or seeing Pokemon dreams. This becomes possible with the introduction of the Dream World in generation V.

Gastrodon and Shellos were supposed to appear in Pokemon Ruby & Sapphire. Due to time constraints they weren't added. Ken Sugimori only did one version of the Pokemon (there are two varieties in Diamond and Pearl).

Nincada is the only Pokemon who will evolve into two different Pokemon at once. When Nincada evolves, if there is an empty slot in the player's party and a pokeball in their inventory, the player will receive both Ninjask and Shedinja. additionally, if Nincada is shiny, Ninjask and Shedinja will also be shiny.

An early version of the Ruby & Sapphire box art shows the version name under the cover Pokemon and the inclusion of the "Gotta catch em all!" slogan. In the final version, the version name was moved to the top and the slogan was removed entirely.

These were the first Pokémon games to have a framerate of 60 frames per second (FPS). This change carried over to FireRed, LeafGreen, and Emerald. However, the framerate was downgraded to 30 FPS in the Generation IV games

Examining the TV in the player's house describes a movie with "Two men dancing on a giant piano keyboard." This most likely refers to a scene from the movie "Big".

This is the only main series game where the player character's biological father is shown. In Ruby & Sapphire, the gym leader Norman is the player character's father, regardless of which gender is selected.

The gems on Sableye's body may be a reference to Pokemon Ruby and Sapphire, as the common colors for rubies and sapphires are red and blue. Sableye's shiny sprite also has green and yellow gems. Green is the common color of emeralds, making this possible reference also line up with Pokemon Emerald.

In Victory Road, there is a one-way ledge on B1F. However, in the Spanish, Italian, French and German releases the top tile of the ledge was removed to allow access either way, and in Emerald, the entire ledge was removed.

Wild Double Battles were planned for Ruby and Sapphire as evidenced by an unused text string found in the game. The string reads, "Wild v[&H05] and v[&H03] appeared!", with v[&H05] and v[&H03] being placeholders for the names of the Pokemon.