Thanks a lot!
The GWJ intro created it a few weeks ago with the intention of using it in my game when the time comes.
The game needs several improvements, including the ball physics.
The ball is a KinematicBody2D because I had collision problems with RigidBody2D.
The music of the intro is a free theme of the great Alexandr Zhelanov.
The rest of the music has been composed by another great composer: Nate St. George, which he kindly gave them to me.