In Act 3 what do Proctor and Mary Warren bring with them as evidence?
Proctor brings two bits of what you might call evidence. First, he brings a petition signed by a bunch of people saying that his wife, Elizabeth, can't possibly be guilty of witch craft. I don't know if you'd call that evidence or not.
The other thing that he brings as evidence is Mary Warren herself. Since so much of the evidence against people has been the word of Abigail and the girls, Proctor is bringing Mary to say that she and the girls have been making it up. So Mary is Proctor's main evidence.