Belli- from "bellicose" meaning the red, rage of hate/anger/war.
-Fer from "bringer"...
= Bellifer… some pretty bashy 40k-ish Latin? LoL
Anyway, the monster turned out to be a pretty low level Challenge as it's basically a nuisance or environmental hazard. But still kind of fun, because it only needs to appear at a distance... in flight no less... so potentially out of view of the players... and strum a few chords to incite rage and mayhem. The effect persists even after the song has ceased but victims get to make a save every round and once they pass a save are immune to that specific Bellifer's tune for 24 hours.