Light Yagami/Harry Potter
In the end, Vernon and Petunia Dursley lived to see another day.
Not because Light didn't want to kill them. On the contrary. They lived because Light found a better, long term plan to cause the Dursleys harm. The loving couple loved to hurt Light by negligence almost as much as they loved to shower their son with affection.
Light decided he would use that. Dudley was only a child. Dudley was barely two then, and barely able to string two sentences along. But Dudley was a very, very affectionate child. he thrived off of his parents attention and adoration and took it for granted at the same time. It said a lot about how much the Dursley couple spoiled their child that Light was able to see these traits in the personality of a two year old.