The discussion of which Mary might be his hunter switch is because it is mentioned somewhere that the identity switch of the deceased can be the character's relative or acquaintance (Alva and Luca for instance although it is yet to be confirmed).
Bloody Queen feels more of a concept rather than a personification, as Frederick didn't really pretended to be her(Joker with Sergi, for example), didn't personify her in a personality disorder(possibly Dolores with Robbie) or ger possesed(possibly Miles with Michiko)
In frederick's case, it is likely because of his purpose to find an item belonged to his late aunt, Mary. Focusing on Kreiburg racecourse, hunter forms mostly came from Alice's subconscious pov and this later forms the theory of Alice seeing Frederick as the hunter Mary (...)
@homewardpath This gamemode feels like a distorted bad memory/nightmare for Alice.
Frederick saving her on the trailer could INDEED mean something... i just wonder how he would get a hunter switch next year if he's apparently the only ally she has