Hello,
According to the help the song of the mist enables the singer and possibly one other character to damage an ethereal or astral mob with their physical attacks. And it works that way with ordinary attacks of all types and with monks' strikes and even with thieves' circle stabs. However it doesnt work with shapeshift forms special attack(I've tested with the equus's kick and griffon's dive). Those attacks keep going through ethereal mobs. Is this behavior by design? Or maybe it could be fixed one day?