All peerless bosses can be barded. Can Provo Satyres on Mel. Bulbous Blobs on Paroxy. Everything but ninjas on Trav at the end. Dreadhorn and Grizzle can be disco'd as well as all the others. I notice that on discord successes the "target shrugs off some of your song" or some such thing. On the Shimmer, you can't provoke anything but the wisps as far as I know. Most of the tags on those green blobs are blue to start. In Shimmer, I run into the hall and target a wisp for first target provo, then go thru teleporter and target Shimmer for second provo target. This keeps the Shimmer at the wall trying to kill the wisp on the other side of it. Is a good way to keep that Shimmer still and in one place. I provo those wisps every chance I get as it seems to produce the blobs which will fight that Shimmer for you.