Arena is a 33 year old being of darkness living in the sonic world. She doesn't have an "other half" like mephiles, granted she doesn't have his malice either. In the public, she will take the appearance of a hedgehog (and much like mephiles, she does have a crystalline form). She has the powers of the element of darkness and (while she hasn't mastered it quite yet) electricity. She may end up creating an arena (much like her name). She may be pudgy, but she has muscle (though it's unknown if it carries over to the crystalline form, appearance wise). A part of her WANTS to teach combat techniques (which may lead into why she wants to create an arena).