While doing the maze I decided to see what happens when I get all the keys. When get one foxy becomes more active. By getting them all a clock hits 12 and a glitched key will spawn. Collect that and head back to spawn to see the bunker there is open. Interact with it like one of the standouts to get your prize.

Mask in maze. https://imgur.com/a/gF1vhcN

After that if you head over to the prize counter you can see the mask in front of the monitor with all the prizes

Prize Counter: https://imgur.com/a/9uTb3aL

To get it can be difficult. You really only need to do this for an Easter egg item, unsure if it has anything to do with what may come.