Order and Chaos 2 is a pretty good mobile game. It's free and it's an actual open world RPG. With people walking around, 3/4 different classes, skill trees, gear actually shows instead of simply changing stats, etc.
If you ever have money to spare there's a pretty cool single player open world RPG sort of like TES called Ravensword: Shadowlands. It's about a good 8-10 hours and can be played multiple times. It's pretty fun. There's a lot of different weapons and while the mobs are kinda bland at first they get more interesting later. How quests are structured are nice too. I was exploring on the coast and found a ship or some shit. Had a ring inside of it, somehow linked to a random side quest in a different town, so that was pretty cool.
Almost forgot dungeon quest. It's a neat and free dungeon crawler. 3 classes that can be played and multiple ways with different elements, weapon rarities, etc. I spent a lot of time on it because my 4G has been garbo. (it's offline)