SpongeBob Production Music | SpongeBob Production Music The Legend Of Boo - Kini Bottom (Unknown track - Halloween variation) @spongebobproductionmusic1081 | Uploaded 6 years ago | Updated 22 hours ago
It's basically this track: youtu.be/2WslTZ4o80E
But with instruments added in the background to make it fit better to the Halloween atmosphere.

By the way, the track also plays after SpongeBob says that he's a lovely flower but it's just few seconds so I didn't want to lose time on fitting that with this part of the track.
I don't own anything.