I have always considered a to be a four footed mammal
The definition of beast is any animal. Pick up a real world Bestiary & you'll find all creatures that are not human. Primates are beasts (2 legs), snakes & worms are beasts (no legs), bats are beasts (2 legs 2 wings). If we r going by the definition of Beast then the spiders & mosquitos are also beast.
Going one step further old world Bestiraies also included dragons so technicaly Vixenatrix is beast.
•Humans/Demi-Humans- are not beasts
•Undead- are not beasts they are unnatural pervesions of life.
•Goblinoids/Ogroids- are not beasts because they have a culture & intellect like early humans.
•Fae- blurred line as some are fae beasts but not all are so...