The song "Dummy!" is a remix of the song "Ghost Fight".
Here is the song "Ghost Fight".
And here is the song "Dummy!".
Spider Dance is also based on this same leitmotif, by the way.
I like how you noticed this stuff. Heres a good reference: Ever notice the death music found halfway through asgore's boss theme? Or floweys theme or snowdin's music or the song Undertale and the menu music found in Hopes and dreams? :D