HT Games
Duplicating Pokemon
You must first capture a Ditto in "Pokemon Fire Red" in the caves at Cerulean. Transfer Ditto to the Daycare Couple in Pokemon Sapphire. Cycle around the area for a while. Circle the daycare until the old man exits the gate and gives you an egg. The egg will hatch into the youngest stage of whatever Pokemon you put in the daycare.
Strong Pokemon
The Pokerus is a glitch that boosts experience points for Pokemon that never run from a battle. If your Pokemon in battle require HP, or health points, use potions to help them but do not take them out of the fight. Do not take them to the Pokemon Center either. They will develop the Pokerus. The virus will spread to all the Pokemon in the party. You will notice a significant increase in their power and health.
Poison Sting
The Poison Sting is an attack for bug type Pokemon. If it is timed right, it will land every time. You must press the "A" button at the exact moment that the bubble passes your Pokemon's hand. The Poison Sting attack does not work on bug type Pokemon.
Floating Battle
This glitch allows you to battle a trainer over water. You must have Pokemon between levels 20 and 30 equipped with Surf and Fly. You must also own the Poke Flute. Fly to Fuchsia City. Head east to the guard tower. Follow the path to the water. Use Surf to glide along the shower. Do not go back to land. A junior trainer will challenge you. After the battle you will still be able to surf.
Thunderbolt
At various times, certain Pokemon attacks like the Thunderbolt can freeze the Game Boy Advance. The Thunderbolt sound effect will continue, but the game will not be responsive. There is no warning for this, and the console must be shut off and restarted.