Having some trouble sorting out things. Like, what is a "mutant" compared to the normal monster?
Just a full body instead of a partial transformation? Wouldn't that make the partials the weaker subspecies? Guessing his sister is alive now. And like a pretty good chance of that. More of a question of if she is an enemy, ally, or enemy acting as an ally.
Oddly, this series is pretty blunt on character work, just the world building seems vague at times.
The idea that humans removed the megafauna is just absurd though. Guessing that megafauna will also be the source of these creatures, by way of Chekhov's Gun.