This character is revealed to have four known identities: Lucas Gottesman, Mona Vanderwaal, Garrett Reynolds and Charlotte DiLaurentis. Lucas wore the costume and called Ali a bitch while wearing it, but he was not "A". Garrett wore this costume on the Halloween Train when trying to warn Spencer about "A". Mona wore it at the Halloween party in 2008 as "A" to scare Alison. CeCe dressed on Christmas 2011.
The costume worn by Lucas can be found at the Warner Bros Museum.
Alison is seen trying to find a costume for Noel Kahn's Halloween bash. While doing so, someone picks up the mask and looks at it. Later, after Alison meets Jenna Marshall, the Baby Mask is standing behind her. Alison then yells "FREAK!".
Later at Spencer's house, all of the girls are getting changed as they spot the Baby Mask outside. When Alison goes to see, he's gone. Aria, Emily, Hanna and Spencer later spot the same costume at the party.
When they go to find Alison at the abandoned house, she says that the Baby Mask grabbed her but she got away. When Alison goes to get a signal in the hallway, Baby Mask attacks and tries to stab her but she gets away. Alison then reveals that it was Noel.
At the party, someone in the Baby Mask costume runs behind Alison and says "Bitch" and is revealed to be Lucas Gottesman, but it is unclear if he was the one that attacked Ali. Then, Noel comes by and says it wasn't him because he had to drive with his brother. After Ali gets a text from "A", there is a bunch of Baby Mask Monsters standing there. One hangs up the phone and takes off the mask. Her identity was not revealed, but it is assumed it was Mona Vanderwaal since she was Alison's "A".
After Lucas talks to Shana Fring, the Baby Mask returns and whispers something to Lucas and goes behind a red curtain. Lucas hands over an envelope and then walks away.
Hanna and Aria spot the Baby Mask at the brew before boarding the Halloween Ghost Train. Aria assures Hanna that it's just a costume and it doesn't mean anything. The Baby Mask is later seen when Spencer is by herself and drags her away, and is revealed to be Garrett Reynolds. No one is sure if he was the one that attacked Alison, because there were more people in the same costume.
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