Pseudumbra Fauxtasm (by Marcy Nabors & Jamie Paige Stanley)
Penumbra Phantasm isn’t on Homestuck Volume 10. But if you really, really want an idea of what it sounds like, there’s pieces of it scattered all over the place.
A few years back Toby played part of it, live, on a piano. This track, Pseudumbra Fauxtasm (alternate title: I Can’t Believe It’s Not Penumbra Phantasm), is a pretty faithful reworking of it. My favorite part’s the break right at 1:25. It’s a bit of the song that isn’t well represented in other mixes, and I love the energy of it.