Monty’s Mystery Mix is one of the necessary items you will need to find while you are trying to survive the night at the pizzaplex. This item is used during the process of decommissioning Chica — you can’t defeat her without it. Here is where you can find the Monty Mystery Mix in Five Nights at Freddy’s: Security Breach.
There are a few steps that need to be taken before you can get the Mystery Mix. First, you will need to get a Party Pass. The first one can be found by breaking into Chica’s greenroom in Rockstar Row. The second one can be obtained in the postgame if you decide to stay in the pizzaplex after 6:00 AM. Once you have a Party Pass, head to Fazer Blast.
Once you are inside Fazer Blast, head to the left and follow the hallway to the security room. Inside the security room, you will find a present that contains the Bowling Pass. This will allow you to enter the Bonnie Bowl on the third floor of the atrium.
Go inside Bonnie Bowl and head over to where the kitchen is. Go to the backroom behind the kitchen and look for a box on top of some filing cabinets. Use the boxes to climb on top of the filing cabinets and interact with the box to obtain the Monty Mystery Mix.