I have an idea for a hard yet easy to execute game-
I was playing Super Mario Maker and I had an idea for a fangame.
What it would be is there would be a procedurally generated castle that had no end, And you would try to survive for the longest time possible, All while it got harder and harder and would change depending on the time of day. People could then share their times online and they could also start exploration parties via LAN/Wireless.