I have been wondering this for quite a while. In the Satanic Bible, under the "Infernal Names", Anton LaVey lists "Fenriz" as the son of Loki, whom is depicted as a wolf. I have looked it up in many Norse Mythology books, and nowhere can I find the same translation for the name. In the old Norse sources, he is called Fenrisúlfr, and often Fenrir for short. The other translations for the name that I have come across are:
Fenris wolf(an English translation of Fenrisulfr)
Fenrisulf (an Anglicized form)
Fenris (not found in the Old Norse sources)
Fenrisulven (modern Norwegian, Swedish and Danish form)
Fenrisúlvur (Faroese)
Fenrisúlfur (Icelandic)

My question is, where did Anton LaVey get the translation of "Fenriz" from? Did he make it up? Or can it be found somewhere? Any help will be greatly appreciated. Thank you and hope to hear from someone soon.