Weirdly enough, I really like Darkness Survival. It's a turn-based dungeon crawler with RPG elements such as jobs (warrior, witch,...), various passive skills, stats, potions, stereotypical monsters (rats, slimes,...), a lot of different weapons, etc...
It's 2D but unfortunately not offline, the map changes every time you start a new run, but there are some things that always stay the same and you have to learn about.
Honestly, its more like an incredibly hard strategy game than an action RPG and I love it for that. It feels like the Dark Souls of mobile games in a crowd of idle this idle that, I've been playing it on and off for years now.
Also, there are no ads \o/