Things You'll Need
Instructions
Insert "Pokémon LeafGreen" into one Gameboy Advance and a compatible game into the other GBA. For the purposes of this tutorial we will use "Pokémon Sapphire."
Connect the two systems by plugging the link cable into the port in the back of each Gameboy unit.
Enter Pokémon Centers in each game and proceed to the second floor.
Enter the trading room and talk to the person at the counter.
Select Kadabra from your "LeafGreen" party and place it in the trading queue.
Select a Pokémon from "Sapphire" to trade for the Kadabra.
Verify the trade by pressing OK on each system.