Pokemon Picross was my introduction to the genre, and I fucking loved it. I played that game religiously when it dropped as a kid, and played it like every day. I just hated how money hungry it was, like their other free 3DS games (Shuffle, Rumble World). Basically any free Pokemon 3DS game was peak in terms of gameplay, but dogshit in terms of monetization.
I still really want a Pokepark, Rangers, or Conquest game 😭
In terms of good mobile games, I didn't appreciate Duel enough before they scrapped it. It was fun and the strategies seemed like they could be super interesting. Plus it has a banger menu theme.