The term creature (and Mark 16:15 could have been added) refers to evil spirits, demons, devils, and so on that inhabit persons such as the seven demons cast out of Mary Magdalene.
In order to free the enslaved of a parasite demon, one must have the authority of certainty of the faith, the certainty of God and his will to liberate humanity. Sometimes this can be confused and extremely difficult as in these days. Lastly, persons can have a physical disease or mental infirmity instead of possession. In this instance, a faith healing maybe required instead of exorcism. Of course, we are mortals and eventually we will die and so will the flock. It is important to know there are limits.

Why could the gospel "be changed?" At my alma mater, the theological and linguistics departments conducted a study of Hebrew versus the English language and Hebrew only had 40,000 words whereas English has many many more words. English does not have words that are part of the ancient Hebrew vocabulary and writers charged with translation tended to "beautify or glorify" the ancient hebrew script to help others better understand what the gospel says.

An example they used was that the original Hebrew of one passage was only 8 words but the translation was two full paragraphs. It meant the same thing, was poetic or alliterated in English, and with the passage of time can sometimes lead to confusion.

Now, when Jesus was born, along with the joyous sounds of choruses of angels, the animals seemed to or were reported to pay homage to him as well. My dog had a pup that was ill and I did espy him doing what appeared to be exhorting God or maybe even praying. I wouldn't doubt it since God can talk to all his creation. Maybe he saw me praying next to my cross enough that...I have witnessed other such instances.