It makes me so happy to know that door got someone lol, I'm also very sorry. It's inaccessible until you've beaten the boss! You also need >85hp, but shhh I didn't say anything. (Or activate invincibility in the dev tools lol). The diagonal shooting is a little rough, and I'm not sure how to fix it, gonna have to mess with that. A few people we're having issues with it.
I'm glad overall you enjoyed it! Nate absolutely killed it with the music, all the praise for that goes to him, he's a legend!