Here's why:
* Arceus wasn't introduced until Pokemon Diamond and Pearl: Arceus is a mythical Pokemon that was first introduced in Generation IV. Pokemon Ruby is a Generation III game.
* Gameshark codes can't add new Pokemon: Gameshark codes primarily work by manipulating existing game data. They can't introduce entirely new Pokemon like Arceus.
To catch Arceus, you'll need to play a game where it's available, such as:
* Pokemon Diamond, Pearl, or Platinum: Arceus is a key part of the storyline in these games.
* Pokemon Black 2 and White 2: Arceus can be caught in these games after completing the post-game content.
* Other games with events or special distributions: Arceus has been distributed in various events over the years for different Pokemon games.
Important Note: Using Gameshark codes can potentially corrupt your save data, so use them with caution.