Obviously Spooktune is in A DARK ZONE, but I think it's actually there from the start instead of starting later in. The opening of the song is just repeating the first few notes of the Spooktune quote over and over again in a different rhythm.
On the left is the opening of A DARK ZONE. On the right is the Spooktune part, with the notes from the opening overlaid in red (with timing adjusted to align with the notes).