Getting Celebi (in Generation 3) | Japanese Colosseum and Bonus Disc
As it turns out, getting Celebi isn't too terribly hard. Yeah, there's a few steps to go through, but this is the most reliable and least convoluted method of getting a Celebi into generation 3.
You will need a few roms, most of them as Japanese versions. Make sure the Colosseum bonus disc is from 2003, and not suffixed with a "v2" on it. That's important.
Serebii.net also has a good introduction on how it's all done as well.
https://www.serebii.net/colosseum/celebi.shtml
You will also need a .gci save file of the Japanese Colosseum game. While you certainly do it normally, there's a user named "Suloku" on GameFAQs who completed the game for you.
Thank you Suloku! (Be sure to check the Japan section of saves)
https://gamefaqs.gamespot.com/gamecube/914973-pokemon-colosseum/saves
0:00 Intro
0:09 Prerequisites
0:55 Tangent: About Memory Card Saves
1:19 Importing .gci Saves (via .Gci-Folder)
1:44 Gci-Folder test
2:01 Importing .gci Saves (via Memory Card)
3:23 Memory Card test
3:35 Using the Bonus Disc
3:59 "Celebi Obtained" confirmation
4:45 Tangent: Backing up our .gci File
4:55 Setting up an Integrated GBA
6:22 Trading to your Gen 3 Game (JPN)
8:13 Removing RTC data (important for certain emulators)
8:56 Testing save file for VBA
9:11 Tangent: Setting up VBA connections
9:43 Trading to your Gen 3 Game (USA)
10:24 Next Video: Celebi in Gen 2