Upon loading into the lobby, press the new button on Mystic Hippo, who will then point you to Sister Location - Office: Puppet Master.

Go into Office: Puppet Master. You will need to type in a code into the keypad inside the drawer on the left of the desk. If you do not already know the code, she will give you a riddle to figure it out. The code is 1979.

After picking up the Tiger plush and quitting back to the lobby, Mystic Hippo will hint at a new performer on stage. Cycle the models on the stage until you can display the Mimic.
Mystic Hippo will then give you another hint to throw or shoot something at it. Doing so opens the double exit doors to the left of the stage. Go through and wind the box to reveal a jigsaw puzzle.

There are 12 total puzzle pieces, one of which you get for free with the puzzle.
You do not need to complete any minigame to collect the piece. Just quit to the lobby after collecting one.
You can click on the images to zoom!

Non-mask lobby - Next to Candy Cadet


Non-mask lobby - On a table next to the hole to the right of the stage.


Staff only - First Aid: Lefty - To the right next to the spray bottles.


Staff only - Fizzy Faz Night 4 - Behind the Sodaroni can.


Staff only - Endo Warehouse - To the left of the camera, on the side of the desk


Backstage - Arts and Crafts: Loft - To the left in the shelf, under the blue paint.


Fazcade - Bonnie Bowl - To the left under the touchscreen.


Fazcade - Fazerblast: Western - To the left under the table.


Fazcade - DJ Music Time: Pro - To the right in front of the car battery.


Ticket Booth - Cinder Carousel - Around the left side of the console toward the back, around head height. The yellow piece is sticking out from behind the clipboard.


Sister Location - Breaker Room - Under the leftmost lever.

When the jigsaw puzzle is complete, a different scene will appear depending on if you have the VANNI mask on or not. Put the mask on to read the code in front of the building (4625) and re-equip the mask to input the code into MXES' box in the back of the van.
Jackie will now be available to display on the stage.