I’ve developed a lot of things for PC (Python / C# / JavaScript).
This is my first android attempt, also the first application created with block based programming!
Keyboard Champ
Type correct and fast to progress through 15 levels!
Always the same 30 words in every round (all players have the same conditions).
I just gave an example. Though you can find ways to engage the users and then come up with in-app purchase part.
The only thing that I was concerned about was the way you are forcing users to buy a ad free version.