Is character assassination agains the law?

In most states, yes. The charge is 'disorderly conduct by abusive language' and in some cases, 'disturbing the peace'. There is also a charge for cursing on a public street.

Abusing or manipulating physically or psychologically somebody, cannot be legalized. We haven't heard about it though.

Ticks and other parasites should be removed or treated as soon as possible as many countries have strict Animal Welfare laws saying that if a dog with parasites is left untreated then it is neglect....

peter ,mollie and chinky

There are no special provisions for fictional characters in current US Copyright Law. They are protected just like any other original artistic work.