Life and Death Totems
Being affected by the corruption might have fundamentally changed what these animals look like on the outside... but it's what's on the inside that really counts. And their hearts have been purified, thanks to the power of the Death Totem.
The Death Raven isn't the source of the corruption - it would never be a part of something that throws the world so out of balance. No, it knows that a small few of the creatures who were caught up in the corruption became used to their new forms, and didn't want to be changed back. They liked being different, and though all creatures naturally hate the magic of the corruption, the new bodily forms themselves are not inherently evil.
The Death Raven knows this, and seeks to right the wrongs by granting a few of their desperate pleas: to be rid of the overpowering corruption, but for their bodies to remain as they are. By using a Death Totem, you summon a corrupt pet from somewhere out there in the wilderness, and the Raven purifies it immediately. It is blessed, not cursed, because it's wish has been granted, and it can now live in peace.
The Life Totem, too, is a beautiful thing, and surely holds more power than all of the individual totems combined. With it you become a surrogate master over the life force itself, and create into being a fresh-faced new companion to your own specifications. The Life Raven in particular celebrates novelty and powerful binding forces, like those found between parent and child, or true friends. Your new pet will follow you to the ends of the earth, if you will allow it.