The Emperor Nero: Viper or Frog?

Toward the beginning of his biography of the emperor Nero, Edward Champlin quotes from an extremely odd reference to the emperor by the Greek biographer Plutarch.  In an essay entitled On the Delays of Divine Vengeance (De sera numinis vindicta), the gods appear to conclude that Nero was not all bad.  While he was a monster who killed his mother, he also "restored the Grecians to their liberty."  It was therefore appropriate to transform him into a frog rather than a viper:

The last things that he saw were the souls of such as were designed for a second life.  These were bowed, bent, and transformed into all sorts of creatures by the force of tools and anvils and the strength of workmen appointed for that purpose, that laid on without mercy, bruising the whole limbs of some, breaking others, disjointing others, and pounding some to powder and annihilation, on purpose to render them fit for other lives and manners.

Among the rest, he saw the soul of Nero many ways most grievously tortured, but more especially transfixed with iron nails.  This soul the workmen took in hand; but when they had forged it into the form of one of Pindar's vipers, which eats its way to life through the bowels of the female, of a sudden a conspicuous light shone out, and a voice was heard out of the light, which gave order for the transfiguring it again into the shape of some more mild and gentle creature; and so they made it to resemble one of those creatures that usually sing and croak about the sides of ponds and marshes.  For indeed he had in some measure been punished for the crimes he had committed; besides, there was some compassion due to him from the Gods, for that he had restored the Grecians to their liberty, a nation the most noble and best beloved of the Gods among all his subjects.