if you're on a PC, you might have to click inside the window after you hit "Run Game" and then press Z or Enter to start the game. Happened to me when i uploaded and a few submissions. Its a bit easier to play on Mobile, since the browser gives you Gameboy buttons on screen.

The engine is GB Studio! its for making Gameboy and GB Color games. The jitter you mean is the camera shake when you get hit? its a feature in the program, i can control how long it last and the intensity of the shakes. but how it does it code wise, i dont know.

The program is doing most of the heavy lifting, it handles a lot of the code, and you can add your own. My coding is very limited; thats why i used this engine. Im sorry if you were looking for a coding answer.