Penumbra Phantasm is a song composed by Toby Fox for Homestuck. The song was never actually released, but its leitmotif was used in many Homestuck songs.
A MIDI and a piano version of Penumbra Phantasm was discovered and is available in the Homestuck Sound Test. Toby also played a version of Penumbra Phantasm on a livestream in 2012.
List of all Penumbra Phantasm leitmotif uses: