The game has 202 Pokémon in total, 135 of which are new.
Jun'ichi Masuda recalls the development of Ruby and Sapphire being very stressful due to the new challenges of developing for the Game Boy Advance and the perceived decline in popularity of Pokémon. Masuda also said he had nightmares of the the game failing upon it's launch.
Within the game's files there's unused remixes of the themes of Pokémon Gold Version (1999) and Pokémon Silver Version (1999), leftover data from testing the sound capabilities of the GBA.
During debugging Jun'ichi Masuda secretly added an NPC to the game named Kiri, a tribute to his then newborn daughter.