Toroom - Well, that ends that run.
What's SUPPOSED to happen is I transition to the next screen, and the music of Level 3 begins playing. What happened instead is that the transition failed, and I was stuck offscreen, unable to move. This effectively ended the run.
What's especially frustrating is that I was paying on Hard mode, which lives up to its name. It took multiple attempts just to beat the second boss. Each level can take upwards of ten minutes to beat, too, if you explore every room. And this is the SECOND time this glitch happened!
I was about ready to give up on the game, but it finally let me into Level 3 on a later attempt, and that turned into a fun run. So I guess I'll keep playing, for now. I'm not sure what triggers this glitch, or if it's exclusive to Hard mode. This isn't the only glitch I've encountered, either. There is a space below the first boss that can damage you for no explainable reason. And menu selections take two clicks to trigger.