You’ll obtain the Tri-Pass right after defeating Blaine in the Cinnabar Island Gym. When you walk outside after beating Blaine, Bill will greet you outside of the Gym and ask you to accompany him to One Island – which is where Celio will give you the Tri-Pass.
If you say no to Bill’s initial offer, he will wait in the Cinnabar Island Pokémon Center until you’re ready.
So you can make your way to One Island and receive the Tri-Pass any time after defeating Blaine.
Since you get the Tri-Pass immediately after defeating Blaine on Cinnabar Island, most of the prerequisites will involve getting to Cinnabar Island and defeating Blaine. Specifically you need:
- HM03 Surf
- Access to Cinnabar Island
- The Secret Key in the Pokémon Mansion
- Defeat Blaine in the Cinnabar Island Gym
If you can reach Cinnabar Island already and challenge Blaine, then you’re good to go.
Just challenge Blaine and walk out of the Gym to get started (or if you’ve defeated Blaine already, walk to the Pokémon Center on Cinnabar Island to see Bill waiting for you).
Getting the Tri-Pass
After defeating Blaine, just walk back out of the Gym. As soon as you step outside, Bill will greet you.
Bill will ask you to accompany him to One Island.
You can say Yes or No here, but keep in mind that you won’t be able to swap out your Pokémon on One Island. So make sure your Party is good to go before saying Yes.
If you say No, you can always head to the Pokémon Center on Cinnabar Island and talk to Bill again when you’re ready to go.
After you say Yes, Bill will lead you to the edge of the Island where the Seagallop Ferry will pull up and whisk you away to One Island.
When you arrive at One Island, Bill will lead you up to the Network Center / Pokémon Center on the north side of the island.
Here, he will introduce you to Celio who is working on a Link Machine.
At the end of this conversation, Bill will ask you to run an errand for him that involves heading to Two Island. This is also when Celio gives you the Tri-Pass.
After you have the Tri-Pass, you can simply head back down to the docks and take the Seagallop Ferries to Two or Three Island.
If you want further guidance for this part of the storyline then take a look at our walkthrough guide here explaining what to do after you reach the Sevii Islands.