Not explicitly Norse but the Celtic chooser of the slain? Sounds like a Valkyrie to me.The Morrigan - Shape-shifting Celtic goddess of War, Fate and Death. Story in "The GODDESSES / Psychology of Female Power"
Griffins are a rare creature that are found in many places on Arda. There are many variances in their coloring and plumage that depend on where they live. They are very noble creatures and are greatly respected by the natural races on Arda.