In threads like this I will always recommend Swordigo. https://play.google.com/store/apps/details?id=com.touchfoo.swordigo

It's an old side scrolling platform game. The gameplay is very nicely balanced so you won't have to grind anything. There's a few difficult jumps and tactics for bosses, but the difficulty increases gradually so you have a good chance of knowing what to do when you get to it, instead of being frustrated.

It takes a few days to 100% it. I think I've done it 3-4 times by now.