I agree. I had a neat idea for it's tendrils to shoot out electricity but it doesn't help that Shub has well.. barely any animation.
A few idea that may work are:
Room shakes caused by Shub, debris falls from the ceiling on you while punchangle is being thrown around (maybe add semi drunk movement

).
Maybe it can turn to face you and manipulate the animation so that it expands and contracts and shoots acidic blood at you through it's "face" ...
but yeah, crappy end boss.