Teen Titans, Vol. 1 #40 (1977) 1st Duela Dent as Harlequin

Daddy's Little Crimefighter
Robin and the Joker’s Daughter escape from Two-Face and warn the other Titans of his plan to blow up both New York and Gotham City. They are delayed by an altercation with the Bumblebee, actually Mal’s girlfriend Karen Beecher in a new costumed identity, but Kid Flash and Mal nevertheless join Robin in time to save New York, while Wonder Girl and Speedy team with the Joker’s Daughter to safeguard Gotham City. Two-Face is reunited with his “daughter” and learns of her crimefighting identity, while Duela takes on a new role as the Harlequin, and Aqualad appears near death after unexplained spells of weakness and unconsciousness during the preceding case.
Release Date: 1977