One thought is going entirely the other direction-- stark, simple.
Instead of: "She was a ruthless, cold killer who sprinkled the tears of babies on her corn flakes and when making balloon animals... she used real animals."
Just something very simple. "It wasn't just that she didn't have a heart. She was hollow."
Let the powerful imagery of a word like "hollow" do your work.
Find that simple word that carries real weight. Not "empty" or "bereft". For me, all on its own, "hollow" conjures up a history, almost a storyline.
Like there used to be something there, but someone else carved it out. Has a sort of brutality.
Often a thesaurus won't get you that word. Maybe seek out the descriptors of animal predators, bacteria, etc. If nothing else, it'll get your mind "river jumping" and may help you get there.