Hi there!
Musical Slugs are orcish music recorded on big, chunky magazines that you can slam into your head-mounted jam players, pop into your Big Robot's music port, etc.
What are you referring to with the "Darkness?" Page number?
Cheers!
ORC BORG and other Mork-Borg hacks let the variable Difficulty Ratings of tests do a lot of mechanical heavy lifting.
Darkness might affect the difficulty of a related test (like trying to find an unconscious orc in a completely dark compartment), but musical slugs- along with any of the other unexplained inventory items- could affect the DR as well (the unconscious orc left their skull-mounted jambox playing when they passed out).
That being said, "musical slugs with greater mechanical effects" is a cool idea! Maybe there are special ones to collect, maybe there's a new character class that focuses on them, or maybe there's a Power that brings them to life. OB is very hack-forward! :D