I'm glad you liked it. Thanks for your feedback!
I really like the idea of a counter for stickers. I'm not exactly sure what you mean by the audio build up, but I'll look into Peggle and see what they do.
Oh it is super simple. If you don't know, Peggle is a arcade/pinball style game where you try to collect points by hitting things with a ball. As you hit more things in a row, there is an audio clip that plays and it gets higher/more intense as you hit more things. You already have a sound play when a sticker activates so making it play a different sound or a higher key would be super simple.
That was just the first thing that came to mind. Feel free to completely disregard my mad ramblings haha.