Oh yeah, I changed the save format slightly, so those broke. It might change again by the final version.
The Intermission 3 music plays at double pitch, so it was keeping the same pitch because the interactions caused by having the fade-outs and songs with intros is kind of complicated, so I overlooked it. The same thing would happen with the fast intro music.
The 4-10 teleport trick is cool. Lowering it to 14, though I expect it'll be tricky for most to figure out. Also, I guess dropping the bomb through the wood doors isn't necessary at all, huh. I could probably force it by adding some spikes, but I won't.
Yeah, I noticed it was possible to get down there too. The top/bottom "extension" blocks have special properties that make them unusable for spells and indestructible - I believe that when they didn't have those, they didn't really behave how you'd expect. Also, I think it's better not to risk bombing out of a screen into an empty void and the game saving there. (While it's not supposed to save in empty screens, there are some screens that need to have a row of void blocks for the correct visuals, so they're not empty.) But yeah, if you could get down to the lower screen, I'm pretty sure you could restart and skip a bunch of levels. I don't know if I want a skip that big, though.
My 4-6 route was bombing past the door, yes. I think it's a lot faster.