GBA Special Features
Game Boy Color games can be played on a Game Boy Color or a Game Boy Advance.
If you play a Game Boy Color game that has a Game Boy Advance Special Feature on a Game Boy Advance handheld, the game may have improved graphics or some new special content.
The Legend of Zelda: Oracle of Ages GBA Special Feature
If The Legend of Zelda: Oracle of Ages (a Game Boy Color game) is played on a Game Boy Advance handheld, a new shop will appear in Lynna Village.
This shop will sell you a Gasha Seed, a Magic Ring, and an Advance Ring, but you can only purchase each item once.
The Advance Ring can only be obtained using this method, and if purchased, it will become the "GBA Time Ring".
References
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