If Sid from Toy Story tortured animals instead of toys, he would be Todd.
Originally friends, Ethan and Todd grow apart, since they have different interests: Ethan likes football, swimming, and fishing, while Todd likes setting things on fire, burning dolls, and playing with explosives. He lures Bailey into his house and appears to have the intention of doing something bad to him, although he never manages to do it. When Marshmallow, another dog in the neighborhood goes missing, we assume Todd made s'mores out of her, although it's never confirmed.
We never see Todd hurt animals. However, Bailey smells Todd's scent on a rock that comes through the family window—and on poisoned meat he finds in the backyard. So if Todd isn't hurting animals, it's not for lack of trying.
After Ethan learns that Todd once lied to Hannah to try and turn her against him, he confronts Todd. "This is why you don't have any friends, Todd. Why can't you just be normal? You're always doing stupid things like this" (14.38). Humiliated in public, and without friends to turn to, Todd lashes out in anger. He burns Ethan's family's house down—and critically injures Ethan in the process, changing Ethan's life forever.
Bailey attacks Todd after the fire is set, and the blood trail leads the authorities to Todd. We never see Todd again, nor do we understand why he was so violent and angry. It's difficult to tell if people stopped hanging out with Todd because of his disturbing activities, or if he took up those disturbing activities because no one hung out with him.
We'd say that maybe things would have been better for Todd if he had had a companion, the way Ethan had Bailey, but for all we know, he did have a dog…until it mysteriously disappeared.