TheHardestOto v1Beta

Click the green box in the bottom right corner to start the game. If you scroll the screen you can see that it says START. It's just poorly placed.

Completed the game now: http://snag.gy/301AT.jpg Keep working at the game, and obviously polish bugs, visual and audio as you get along. So far it was a pretty addictive platformer. Good luck!

I've just tried the game on a different computer, and it seems like the screen size problem is different for different resolutions. You might want to look into that.

After one more hour, I've made a bit of progress (I died to the invisible spikes where I painted the red cross): http://snag.gy/i9hXW.jpg

I've been playing this game for a few hours. I'm able to get to the jumpy mushroom area pretty much every time now, but I haven't gotten further than to the first upper platform in it, between the two visual spikes in the top wall.
Overall, it has been a pretty fun game. But obviously there's great visual flaws, but that's less important for a beta. The greatest hurdle was the scrolling problem, and the fact that the "Start" button for the game, is kinda hidden, unless you scroll the game screen.
I thought the game's mechanics were decent and the difficulty curve was alright as well. It must however admit that it has gotten a bit tedious to do the same thing over and over again. My brain starts to shut off from boredom in the first parts of the map and I begin making stupid mistakes. 3/5 for a WIP beta. Keep at it.