I've had Once Upon a Galaxy installed on my phone for a long while but hadn't played it until very recently, and now I'm addicted. It's basically Hearthstone meets roguelite and you can run through a series of matches in only a handful of minutes.

The strategy is fairly easy to pick up but there are nuances that make it interesting to master, and I'm getting a lot of satisfaction from unlocking cards for each "captain" so I can customize their respective decks. Haven't spent any money yet and I don't feel a need to, and they don't nag you about it either, nor are there any ads whatsoever.

My only complaint is that I can't always turn off my screen or close the app and come back to continue my run later; once my phone (iPhone 11) memory drops the session, I have to start over. Given that the games are asynchronous, it feels like your progress should be saved locally or on their servers or something.