Mutations.
Evolutionary paths determined the internal structure of a beast, and if it was humanoid, it would have a Class like humans, Sif and Giants, but if it was not, it would have a mutation instead.
A mutation was a sort of a unique bodily trait outside the bounds of abilities exclusively granted by virtue of being part of a particular species. Unconventional mix breeding, consuming other outlandish beasts, and coming into contact with mystical geographical phenomena were a few of the ways mutations could be born.
Thus, like Classes, there was an unlimited assortment of mutations.
That said...
'Is the set of abilities from this creature something from a mutation? It hasn't shown anything unique besides being fast and having sharp claws,' Skullius wondered.
