Some players confuse Tekken Tag Tournament (2000) with Tekken Tag Tournament 2 (2012). For TTT2 on Xbox 360/PS3/Wii U, the unlock process is different. However, for the original TTT, modders have created "Arcade Edition" patches that enable the boss characters (Unknown, True Ogre) from the character select screen.
If you want the ultimate all-characters-unlocked experience without emulation, consider Tekken Tag Tournament HD (available on PS3 PSN). Using a save editor like BruteForce Save Data, you can unlock everything in 5 minutes.
If you own the original disc or a digital copy, follow this guide. Tekken Tag Tournament All Characters Unlocked Download
If you want to play on a real PS2 with a disc, use a cheat device.
Step-by-step:
Note: Gon is sometimes excluded from cheat codes. For Gon, use a save file instead.
When you successfully download a version or save file with "All Characters Unlocked," you gain access to: Some players confuse Tekken Tag Tournament (2000) with
Having these characters available from the main menu transforms the game. You can immediately jump into tag combos with Devil Kazuya and Angel, or test the bizarre synergy between Gon and True Ogre.