Martha is a snake caught by the god Hermes. She is immortal, though she isn't a monster. Demigods and gods can hear her speaking to them in their minds. Martha is always seen with her male counterpart and husband George.
Obviously, don't nominate any human characters. Hybrids like Cheetah or The Lizard are okay, as are shapeshifters with one set animal form (eg Professor McGonagall.)
