A player in my saga would like to play a Nightwalker as a companion - a lady from a noble family whose scions have always defended the land Nightwalking against various supernatural threats.
For a number of symbolic, story-related reasons, it would make a lot of sense for the shape to be a gryphon. But in general, Nightwalkers who take animal shapes are supposed to take those of mundane animals. Do you see any fundamental problems (thematic, mechanical, etc.) in allowing a gryphon phantasticum - obviously without any MR? It might be a little stronger physically than, say, a lion or a bear, but given that in principle phantastica can even be whales...
Also, the player has proposed that in said tradition the captain is the only "true" Nightwalker; but that by making other characters stray as per the usual rules, the captain can gather them as a small host to aid it in its battles ("When in spirit form, guided characters have all of the powers common to nightwalkers" HMRE p.108). Is this reasonable? Or am I missing something that might be problematic? I find the Nightwalkers chapter not as clear as others in HMRE, unfortunately!