No, there isn't another level. The challenge was supposed to increase by having more frogs spawn, but during a bug fix I accidentally removed the line of code that started the timer to spawn additional frogs :/.
I agree, the bonuses are too difficult to get. They should probably only spawn on roads and rivers, and have a signifcantly longer lifespan, the idea was to use cars to push the tokens around, or use logs to make the frog collide with them, but they only last for like 5 seconds so its pretty much impossible.
The combo is a multiplier that increases with every frog you get across. It would have had a much bigger role if there were multiple frogs on screen, but alas.
Thank you for your feedback! I also wanted to let you know that you posted your comment twice. If you didn't know, if you try to post your comment without saving your rating first, itch IO will still post your comment even though it stops the page from loading to remind you to save your rating.