1. Mona makes out with Caleb to help trap 'A'.
When the Liars thought Spencer's sister, Melissa, was 'A', they devised a plan to expose her which involved Mona making out with Caleb. Mona did this to help protect Hanna but it was a pretty bold game plan!
2. Using code to warn Hanna and the girls in 'Crazy'.
OK, so Mona chose the creepiest way to warn the girls BUT it was so sweet that she used the code she and Hanna shared as BFFs.
3. Destroying Caleb's 'I love you' letter to Hanna.
Was Mona trying to protect Hanna or was this just jealousy? Either way, this one is pretty much all enemy.
4. Mona is 'A'?!
At the end of Season 2 Mona was revealed as 'A' and admitted tormenting the Liars because they ruined her friendship with Hanna. Diagnosed with a personality disorder, Mona was sent to Radley for treatment.
5. Competing against Spencer to be captain of the decathlon team.
Spencer was pretty devastated when Mona beat her, and although we felt bad for Spence, this is literally one of our favorite frenemy showdowns of all time!
6. Casually drinking Spoby's anniversary wine in Toby's apartment while Spencer cries at the door.
Not happy with ruining high school for Spencer, Mona also wanted to destroy Spoby. Even by Mona's standards this was a whole new low. Not cool Mona, not cool.
7. Taking the blame for Detective Wilden's death.
When Hanna's mom was arrested for Wilden's murder, Mona convinced the police that she was the one who killed him, much to everyone's surprise...
8. Telling Aria to 'suck it up'
Aria really wasn't happy about her little brother, Mike, dating Mona. But Mona stood up for herself and questioned why the Liars shut her out after she put herself on the line and tried to take the fall for Wilden's murder.
9. Escaping from the Dollhouse
Although Mona was forced to torment the Liars by dressing and acting like Alison in the Dollhouse, she always tried to help the girls escape. That was until she was put into The Hole by 'A'...
10. Helping Spencer and Toby find Mary Drake's Radley file.
Mona had a habit of appearing EVERYWHERE in Season 6 but she wasn't always a welcome guest. Remember Caleb's reaction when she appeared at the motel after Hanna's kidnapping?!
Mona has had SO MANY frenemy moments! Which one was your favorite? Let us know in the comments!