Likes: Strife, humans, having limbs
Dislikes: Fighting, saints, deities
Talents: Being a bad influence
The Serpent of Eden, who convinced the original woman to taste the forbidden fruit, thus causing mankind to become tainted with the Original Sin and be expelled from the Garden of Eden until the end of the world.
Envious of God's youngest, who were made in his image, the Serpent made the corruption of humanity her sole function. A cunning and vile creature, that relishes in bringing to the surface the evils that dwell in the hearts of men, leading others astray with nothing but words, without them ever realizing, and then smugly smirking from afar as she sees what suffering this brings, while her own hands (sic) remain clean. To her, there is no greater pleasure than to see a supposedly good person commit some manner of atrocity, not because they were forced to, but because they had this potential all along. All they needed as a little "push" from her.
However, if one of her targets to torment genuinely accepts their evil, instead of hypocritically denying it even as they fall deeper into darkness, Nahash will genuinely accept them as a fellow fiend, and consider her job done. By that same measure, if she truly finds a heart without any disposition for evil, any interest she has in the person will turn to anger and frustration.
Though her association with the Devil is due to popular misconception, she readily accepts the results - particularly the ability to shapeshift, as it lets her circumvent some of the effects of God's curse. In a Grail War she is likely to attempt to (and probably succeed in) making a pact with another team, working together to eliminate others first, all the while sowing distrust among the pair that joined hers so that by the end of it she won't even have to kill the last remaining Servant.