How to Get Larvitar in Sapphire

Play through "Fire Red" or "Leaf Green." Speak to Bill at the Cinnabar Island Pokemon Center after you defeat the Elite Four to head out to the Sevil islands. You will arrive at One Island and meet Bill's friend Celio.

Complete the errand he sends you on by retrieving a Ruby from the mountain to the north of the island. He will inform you that you need the Sapphire as well to fix his machine. This is crucial as it will allow you to trade Pokemon to and from the "Ruby" and "Sapphire" versions.

Go to Six Island, head east of the Pokemon Center, then south to enter Ruin Valley. Make your way to the center to reach a door. Use a Pokemon that knows the Cut move to open it and go inside.

Climb down the six levels to reach the Sapphire, but before you can take it, Team Rocket will swoop in and steal it away to their Hideout. Leave the cave.

Travel by boat to Five Island and enter the Rocket Hideout. Work your way through the Hideout and defeat all of the trainers inside. When you defeat the final one, you will receive the Sapphire.

Return to One Island and give the part to Celio. When the machine is fixed, travel to Seven Island.

Walk south on Seven island as far as you can, then head east to reach Sevalt Canyon.

Run around in the grass until you encounter Larvitar. Battle it, weaken it and capture it. Make your way to a Pokemon Center and make sure Larvitar is in your party. Head upstairs to the Union Room.

Attach the Gameboy Advance Game Link Cable to each system. Make sure it is secure before talking to the attendant and entering the Union Room.

Check that your friend with "Sapphire" is in the Union Room and talk to them. Select Trade from the options that appear. When your friend confirms the trade, select Larvitar for trading and wait for your friend to select a Pokemon to exchange with it. Confirm the trade and this will send Larvitar over to the "Sapphire" version.