3. The Joker and Harley Quinn
This pair needs no introduction, as they are two of the most famous and most popular villains in comics. People
love these characters, so an animated feature focusing solely on them would be a welcome addition to DC's library. Harley is fairly new to the DC universe, first appearing in Batman: The Animated Series in 1992 before being brought in to the comics a year later. Dr. Harleen Frances Quinzel was an Arkham Asylum psychiatrist, who becomes fascinated with The Joker while interning at the asylum and volunteers to analyze him. She falls madly and hopelessly in love with him, and helps him escape. When he's brought back in by Batman, badly beaten, it drives Harleen insane and prompts her to take up the identity of Harley Quinn. The love affair between the Joker and Harley is legendary, and Harleen's story would make for a great animated feature. Yes we've seen much of it already in the Animated Series, but perhaps it's time to update the story and dive into it with more detail.