Isso é difícil, pois é um tropo de ficção científica muito popular, mas vou enviar Stinger por Robert R. McCammon. Publicado no final dos anos 80, é sobre (ênfase minha):
Ever since the copper mine closed, the West Texas desert hellholes of Inferno and Bordertown have been slowly dying. Snake River isn’t the only thing that divides them. Racism, gang wars, and anti-Mexican sentiment have turned the sun-scorched flatlands into a powder keg. If anything can unite them for now, at least in awe and wonder, it’s the UFO that comes soaring out of the clouds like a flaming locomotive.
In the wake of the crash, a young alien named Daufin has arrived, too. A fugitive who has taken the form of a human, she knows the terror that awaits the inhabitants of this planet—because it is looking for her.
When Stinger, the monstrous alien bounty hunter, arrives, it’s with a destructive fury and a devious plan to find Daufin—by entombing the residents in an impenetrable and inescapable dome. A relentless killing machine, Stinger has an infinite capacity for death and destruction. And over the next twenty-four hours, this town is going to bleed and burn. Now, the few remaining survivors must come together to protect Daufin, themselves, and the world beyond from total annihilation.
O alienígena caçador de recompensas é meio que um escorpião gigante, não me lembro se ele tem alguma capacidade de mudar de forma ou sempre se parece com isso. Daufin pode definitivamente mudar de forma para um grau.