Many of his shots are easy to dodge given how slow they are, and even the wavy shots aren't too difficult to dodge. The boss itself isn't super difficult to fight early on, even if you don't have the most amazing damage output. If you've defeated him before, then a ray of light and a trapdoor will spawn that lead to the Cathedral and Sheol, respectively, if you have unlocked them. The first time you defeat the Hush, a golden chest will spawn in the middle of the room that you will use to end the run and gain Ending 17.