Let's go on a quest!
I swear I vaguely remember that the VGMDB page for Free Pl@ying used to mention something about びっくりさせたらおこるよ！ being a cover of Happy Halloween Maria.
There's no information about it on the page itself, and I doubt it's actually the case, but there must have been something, somewhere that caused me to create this little mashup I found on my hard drive... Let's find out what it was!