The Riddler
We don't see Paul Dano's face in the first trailer as the Riddler (alias of Edward Nigma), but we do see his handiwork. The trailer kicks off with a masked man duct-taping his victim, and it's later heavily implied that this was the Riddler. We also see one of his creepy notes delivered to Batman, reading in part, "Haven't a clue? Let's play a game, just me and you," followed by a set of cryptic symbols.
At DC FanDome, as reported by Collider, Reeves had this to say about this early-career Riddler: "Paul Dano plays a version of The Riddler that no one has ever seen before. He's such an incredibly creative actor, so what he's doing I think is going to blow peoples' minds... The Riddler is just emerging for the first time."
Image Source: Warner Bros.