So I've been thinking more about Deep Ones now I've rediscovered my ArM5 books during the recent move, including the latest of the 3 "Shadows Over Innsmouth" anthologies edited by Stephen Jones. I've managed to look over some of the notes on concepts I scribbled down in response to the Fomorach material in The Contested Isle: the HIbernian Tribunal.
As mentioned in a previous post and the poll I ran about a year ago on the Forums here, modelling Deep Ones in Mythic Europe presents certain challenges, but the consensus is that portraying them as a type of Magic Human (and their hybrids as Magic-kin) is the best way to mesh the established Mythos concepts with the default Mythic Europe paradigm. I'm still keen to explore portraying the fish-frogs as Faerie creatures to suit some story concepts but I've therefore developed Deep Ones as a form of Magic Human in the following article :