Haha, I can't believe you found Mario! I think you might be the first or only person to do that. Excellent work.
The secrets exist to unlock a final world of ludicrously difficult levels. In the full version you would be confronted with an end screen where you can go right to the Exit for the basic ending or head left through the secret door (provided you had found all the purple screens) and take on the final 10 levels.
I'm not actively working on the full version of Blake at the moment due to a couple of different external factors but it is something I would love to come back and complete one day.
Thank you for your kind words and I'm really glad you enjoyed the controls and the movement - it's the part I was most focused on when I made it.