Fun little game!
Attacking up and down would be cool and bouncing as the tornado.
What do you mean by "bouncing as the tornado" though?
For example, if you come from the middle to the left, after hitting the wall instead of going directly back to the middle you could move up or down and then back to the middle. This would take a bit more controll and would make it easier to hit the boss. It also would make the boss fight less monotonous.