Gorillaz: Driven by greed and desperation, psychotic bassist Murdoc slowly became more unhinged with the Plastic Beach arc. He rants and raves aimlessly in his radio broadcasts and seems to be loosing his grasp on reality, and he no longer bothers to hide his criminal activity and blatant abuse of his "friend" 2D. The 'villain' term might be a little iffy, as Murdoc's still more of a Nominal Hero than anything, but he's definitely got some decay going.
The sadistic autocrat in Judas Priest's "Tyrant", who starts out as a ranting megalomaniac and becomes more barbaric as the song rolls along, until in the final verse he senselessly hasall his own soldiersexecuted. Made all the more effective, of course, by Rob Halford's lunatic screams.