Dr. Jonathan Crane, also known as the Scarecrow, would have been a character in the DC Extended Universe, specifically appearing in the 2016 film Suicide Squad. His role is largely unknown.
Very little is known about the role the Scarecrow would have played in the film. He likely shard his comic book counterpart's origins of being a fear-obsessed psychiatric doctor and scientist who develops a toxin that causes panic, paranoia, and realistic hallucinations, and uses it to commit crimes and test his victims' psyches.
It is possible that the Scarecrow could have been the original main antagonist for the film, as he has yet to be a part of the titular Suicide Squad in the source material. This role would later be given to The Enchantress. The Scarecrow appearing as a character in Suicide Squad seemed to have not made it past the concept phases, though concept art exists of him wielding a sickle.