What would this do?

[Proginoskes]

Well, ignoring the nonsense refrain, it's an obnoxious song about obnoxious songs, so probably something like "I'll Play For You", but with greater range and good for offensive abilities. To push it towards game-breaking, it could turn his next song into an Ear Worm, and for a week, trigger some effect whenever the subject sings it to him- or herself. (For example, Doug targets an enemy with the Chicken Song, then plays "Lightning's Hand". Three days later, that enemy finds himself singing "Can you see me?/Do you know my position?", and is then struck by lightning out of a clear blue sky.)