wickedcestus 🏆️ That’s it! 🏆️
Each game introduces a new non-playable character who becomes playable in a later game:
- Sonic 2 (SMS) introduces Tails who goes on to become playable in the Mega Drive version released shortly afterwards.
- Metal Gear Solid (or Ghost Babel depending where you live) on GBC introduces Jack/Raiden who is playable in MGS2.
- Tempo's girlfriend Katy is introduced in the first game but becomes a playable character in Super Tempo.
- The shopkeeper Hachi from Advance Wars is a playable CO in Advance Wars 2.
- Onikage from the first Tenchu is playable in Wrath of Heaven.
(As for the extra bonus clues; Mario Galaxy introduces Captain Toad and Rosalina, Metal Gear introduces Big Boss and Gray Fox, and Sonic CD introduces Amy and Metal Sonic.)