Two hours later…
… I have only a set-up system and a scaffold of a 2D sprite system.
This is getting hard. I have a nice and simple idea, but I’m too slow coder. Sigh. I’ll try to have a small submarine the player can control and few obstacles before this night. If I can’t, then I’ll not be able to finish. 
Also, I see some stuff around and wow! Just wow!