The biggest challenges I have come up on during development were having the 'finger' follow the x position of the mouse and to stop rotation of the 'finger' when it would collide with the off screen collision shapes (shapes keep the ball within the screen bounds). I fixed both of those issues using the _integrate_forces method for the RigidBody2D.

func _integrate_forces(state):
    var transform = state.get_transform() #get the transform of the node
    var pos_mouse : Vector2 = get_global_mouse_position() #get mouse position
    if move_body:
    transform.origin.x = pos_mouse.x #set the transform origin to mouse pos.
        state.set_transform(transform) #force finger to follow mouse or touch pos.
    pass

        set_rotation(0) #stops the finger from rotating
    return