Yup, Lupa already fills this role.
Here is her flavor text: "A spectacle and executioner, Lupa is often brought into the arena to finish off foes who have been condemned
, or to rouse a crowd when their interest is flagging. Crushing the heads of the fallen with great strokes of her hammer
, or toying with opponents by incorporating elaborate flourishes, she ensures that even the most lackluster opponents will be drawn into a great show. Adept at creating a captive audience, Lupa ensures that the crowds always leave satisfied."http://arenarex.wikia.com/wiki/Lupa