The Legend of Zelda: Oracle of Ages and The Legend of Zelda: Oracle of Seasons are both now available on Nintendo Switch Online
The two games were released on the same day in 2001 and are two completely separate games that link together. They're also the directorial debut of Hidemaro Fujibayashi, the man behind The Legend of Zelda: Breath of the Wild and The Legend of Zelda: Tears of the Kingdom, two of the most beloved games in the entire Zelda series.
While a common misconception is that The Legend of Zelda: Oracle of Ages and The Legend of Zelda: Oracle of Seasons are similar in nature to Pokemon games, with only small changes between the two titles, that actually couldn't be further from the truth. Both games have different central mechanics, and if you play one of the titles after the other using a password provided to you when you complete the game, you discover a brand new ending and a new boss for Link to fight.
In order to access these two titles you'll need a Nintendo Switch Online subscription, with extra titles for Game Boy Advance and other systems available if you upgrade to the Nintendo Switch Expansion Pack tier.