Many are aware of Harley Quinn’s relationship with The Joker, staying by his side since the very beginning in Batman The Animated Series. However fewer people know that she also has a love relationship with the villain Poison Ivy. Within the Injustice comics, it has been eluded to that the two women have gotten married in Las Vegas. But it wasn’t until Injustice: Year 0 do we see actually see Harley Quinn and Poison Ivy get Married.
The story begins with The Joker getting his hands on an amulet that allows him to control people’s minds. At some point, he uses this power to force his sidekick Harley to jump off a balcony, injuring herself. Harley has a moment of clarity and decides to leave Joker while breaking Poison Ivy out of prison. Without a proper hideout to retreat to, Harley visits her sister’s home because she is taking care of Harley’s child. Her daughter at this point is a toddler but is seen sleeping next to a toy car with a tutu on it, a reference to Injustice Year Two. When Harley asks Red (Poison Ivy) to watch after her daughter if anything bad happens to her, She decides to take action and visit Joker. He is sleeping and doesn’t have the power of the amulet. Poison Ivy threatens him and makes a lot of derogatory comments.
In the morning, Red returns to Harley Quinn and they decide to go to Las Vegas together. They stay on the top floor of the Metropolis Casino. Harley predicts their inevitable paths of self destruction while talking alone. After Harley spends some time using the slot machines in the casino, she comes back to her room to discover Poison Ivy in a dress. Along side her is Harley’s sister and daughter, and an Elvis impersonator. She asks Harley to marry her, and she responds with an enthusiastic confirmation. The last panel, of course, has them kissing.
This monumental kiss solidifies their relationship and can be see in Injustice Year Zero issue 8. However I recommend picking up (Affiliate Link) the trade paperback that includes all the issues.