Pokemon Crown is a romhack that basically serves as an all-new medieval JRPG, reimagining classic Pokemon with new combat and catching mechanics.
Set in a medieval Pokemon region called Gueldar, Pokemon Crown puts you into the boots of a Pokemon trainer out to win the appropriately-named Crown League. As a romhack, this is essentially a conversion of Pokemon FireRed on the GBA, but it's been transformed into a whole new game, with an original region, new sprites, and refreshed UI.
But the biggest change in Crown is the new battle system. Drawing inspiration from games like Auto Chess and Teamfight Tactics, the traditional turn-based combat has been turned into an auto battler. You place your Pokemon on a grid and they automatically battle the enemy team - the strategy is in building your team and placing your creatures. There's even online PvP, which is particularly impressive for something that's technically still a GBA game.
A beta version of Pokemon Crown hit the project's Discord server (opens in new tab) two weeks ago, and it's been thoroughly impressing Pokemon fans and content creators since. There are plenty of Pokemon fangames and romhacks out there, but few as impressive as this, and official or not this is the most exciting Pokemon spin-off I've seen in a long time.
You can naturally play Pokemon Crown for free, which is a genuine deal compared to your $10,000 Pokemon Yellow options. US customs probably won't even destroy this one.
If you really want something to battle over, check out our ranking of the best Pokemon games.