Good news: he's just a pre-order bonus.
US retailer Best-Buy has confirmed the character's appearance in a listing on its website. The irritating side-kick will be playable on two challenge maps if you pre-order the game from Best-Buy. Neither Warner Bros nor Rocksteady has confirmed the listing, which has since been pulled from Best-Buy's website. Thankfully the fine folks at ArkhamCity.co.uk caught a snap of the website in time.