We know that they can destroy almost any uncroaked by hitting them. Ansom discovered this power himself. They can apparently also do some other combat moves, like when Wanda grabbed Ossomer's sword with them.
We have not seen any music, rock or otherwise, from the 'pliers. My own little pet theory is that they can be played like a harp.
I always figured that the power to destroy undead was just normal artifact weapon based damage, seeing as how Ansom wasn't atuned.