[@Grnmachine] Here are the things we decided should be required for the viola as we saw some ways it could be abused and we want to make sure it isn't too OP:
So a big thing is that your character will need to maintain eye contact on the beast, his full concentration needs to be the creature, if he looks away the spell breaks or if he loses sight of the beast somehow (like by attacks from other chosen) the spell breaks.
Another thing is that if there is a loud noise that interferes with the music being heard the spell is broken.
Finally and probably most importantly, it has no effect on the bigger creatures/beast especially the Hunters and Guardians(you will learn more about those when the bestiary is shared within the ooc post).

I hope that you understand where we are coming from as sometimes this could make things a bit boring when involving creatures that don't travel in packs or such. We all truly love the uniqueness of the viola and are excited to see how it plays out as long as these guidelines are followed.