Malamber
What about pokemon and digimon transformations? And if the knowledge from another world's species works can't any imagined species work? What about ben 10 aliens, marvel mutants, inhumans?
By the way he should be able to transform into anything if he becomes ditto from pokemon not just beasts like different kinds of item like plane, gun, etc. Can he combine ditto and upgrade from ben 10 into a more powerful race? It would be OP like would he be able to just upgrade races?
Malamber:Off hand i would say Mutants and Inhumans would be a no go because at their base that are still human and his human form is Gar. Ben 10 aliens would probably be redundant because of all the alien life in this universe. Like I have said before Imagination will be a major key in the later transformations but the MC hasnt watched every bit of Anime or cartoon out there. Sorry to say but his imagination will be limited to mine with help of my readers.