In Japan, Sega Ages Gain Ground launched on December 27, 2018, and a release date for Sega Ages Puyo Puyo has yet to be announced.
Here is a brief overview of each title, via Sega:
Gain Ground will see the addition of an All-Member Mode that unlocks all 20 characters, along with an Easy Mode if things are a little too difficult or you simply want to enjoy the game casually.
Meanwhile, the Sega Ages release of Puyo Puyo will allow you to try your hand against other players outside your home with Online Play while testing your skills on the leaderboards with the new Ranking System! Note that Nintendo Switch Online is required for online play.
Other Sega Ages titles planned for release in 2019 include Alex Kidd, Columns II, Puyo Puyo 2, Space Harrier, Virtua Racing, Sonic The Hedgehog 2, and Thunder Force AC.