I think I finally got it!

After some research, I think I got the best difficulty curve for the game.

Reading about incremental games gave me a grip of what I should do with the math, and to be honest it was fairly simple.

My main concern now is the time between each temptation pulsation, I'm trying to keep it fair and fun by doing small increases between pulsations each time the ad appears on screen. In all honesty I would like to implement a more elegant solution for calculating the time and keep the game challenging the more coins are collected, but I don't know how to achieve this, yet.

Attach to this post is the latest version of the game with the changes implement, give it a try! Feedback is appreciated.