I don't understand the oxigen part but the game is working and Pong is always fun ! 

Classic! I really like the baackground. It wouldd be cool to see it animated as well!

Heyy! This game is really simple, yet I was hooked. It sadly doesn't really fit the theme for me. And also for a restart button, you could create a button, attach a script to the button or some node, connect the button's pressed() signal to that node, and in that function just do get_tree().change_scene_to_file("path to scene you want to change to"), or much better, in that function, do var next_scene = load("path to scene you want to change to"), and then get_tree().change_scene_to_packed(next_scene). Hope this helps!

Hi. 

Very nice take on a classic game.

The underwater theme is very calming.

Something weird happened, the ball pushed me away from the bubble, even through the wall behind me.

But very entertaining, 

Here is our game. If you would like to give it a go, a review would be greatly appreciated =).