I'm sorry, I don't see why anyone wants Scarecrow in the game, he seems like more of a manipulator rather than a fighter.
Believe me son, Scarecrow as a fighting game character has a lot of potential.
Scarecrow knows how to fight. He is the master of the crane kung fu! I'm serious.
But even though he actually knows martial arts, I would like to see him as a person who simply doesn't know how to fight, so he attacks very wild, very furiously with throwing fists and kicks everywhere.
He could use his needle-claw-hands, that he had in Arkham Asylum, or he could use a big scythe, or 2 smaller ones, whatever he likes.
Additionally to that you have a lot of cool stuff he could make with his fear gas to have various visual stuff like creatures, damage over time effects, debuffs, maybe even a paralyzing stun.
His super would be his Scarebeast form, where he transforms into a large ass beast, that is able to tear some shit up: