Choosing a Starting Pokemon
At the start of Pokemon Ruby, you will choose one of three Pokemon as your starter. This Pokemon always has the chance to be your strongest Pokemon as it will be with you for the entire game, unless you trade it. Choose your starting Pokemon with the mindset that this will be your greatest ally.
The following are the starter Pokemon in Pokemon Ruby:
Treecko: A Grass-Type Pokemon that is also competent with physical attacks. At level 16 it evolved into Grovyle and then into Sceptile at level 36. Strong against Ground-Type, Rock-Type, and Water-Type Pokemon but weak against Fire-Type and Ice-Type.
Torchic: A Fire-Type Pokemon that is resistant to Ice-Type and Grass-Type Pokemon but is weak against Water-Type and Ground-Type. Evolves into Combusken at level 16 and at level 36 will transform into Blaziken.
Mudkip: A Water-Type Pokemon that is effective against Fire-Type and Rock-Type Pokemon but is weak against Electric-Type and Grass-Type Pokemon. Will evolve at level 16 into Marshtomp and then into Swampert at level 36.
Double Battles
Pokemon Ruby and Sapphire are the first games in the Pokemon series to feature double battles. These battles will have two of your Pokemon facing off against two opponents, which brings a new level of strategy to the game. Having two Pokemon of one type will leave you at a disadvantage if your opponent has varied his Pokemon-type. For this reason, always keep Pokemon of opposing types in your inventory. For example, if you have a Rock-Type Pokemon in your party, also keep a Ground-Type Pokemon. This way, when you're in a double battle, you're likely to have a Pokemon that counters any strengths of your opponent.
Double battles are especially useful in gaining experience points for your Pokemon, as they fight twice the Pokemon than during a normal battle. Switch out Pokemon during any battle you feel confident winning to spread the experience around. Furthermore, teaming a higher level Pokemon with a lower level Pokemon can help boost the weaker creature. Keep in mind that your weaker Pokemon also risks taking damage from two Pokemon so determine if the risk is worth the experience reward.
Exclusive Pokemon
Much like other games in the Pokemon series, Pokemon Ruby has several Pokemon that can only be found in this version. Capturing these Pokemon can be useful in trading as players without Ruby will have no other way to obtain these Pokemon aside from trading.
The following are the exclusive Pokemon and their location in the game:
Groudon: The mascot of Pokemon Ruby, it appears on the box art of the game. Groudon is a Legendary Pokemon that can be found within the Cave of Origin. Only one exists in each game, so make sure you catch it when you meet it.
Seedot: Common Pokemon located along Route 102 and 104.
Nuzleaf: Route 114 is home to Nuzleaf.
Shiftry: Must be evolved from Nuzleaf.
Mawile: A common Pokemon that can be found within the Granite Cave, Cave of Origin, Victory Road, or the Sky Pillar.
Zangoose: Hunt along Route 114 for this uncommon Pokemon.
Solrock: You'll find Solrock in Meteor Falls.