Joker gave a quick smirk as the door flew open. The cell was empty, now, giving him a way out. Gotham would soon be his for the taking. Before he could really get anything out, however, Harley has rushed up, and embraced him with a hug. He didn't really hug her back, as this type of affection wasn't really "comforting" for him. He wasn't big on hugs and love. He just knew one thing: chaos.
SHe ran off, leaving him with the keys, the card, and the passcode. Pretty much, Harley gave Jooker everything he needed to get a good escape, and let loose all of Arkham. That was nice of her. That meant that not only was Joker getting a city, but he'd be able to let loose all of his psychotic companions along with him, starting with...
He gradually approached the cell before him, containing the fair Doctor. He crouched down, getting to eye level with the man. He could see it. The insane "clown" could see the derranged life of the doctor right before him. His life was filled with fear and paranoia. Yet, it was those two very things that he used to his advantage. Unfortunately, Joker didn't really even think about fear. Joker wasn't afraid of anything. In fact, he would barely think enough to even think to be afraid.
"You look a little down in the dumps doc. Here, this might help ya out a little." He stood back up, keeping his posture once more. A quick turn of the key, slide of the card, and typing of the pass code, unlocked the cell containing the man. The door uncleanched, unleashing its locks, and freeing the being inside. He took a grasp of the door, and slid it open to the outside, giving him a perfect view of the doctor. "Your expertise is making people afraid, and throwing their lives into mayhem...I like that."