Big Squeeze is the fourth mini-boss fought in Sonic Mania, encountered at the end of Flying Battery Zone Act 1. It is loosely based on the Barrier Eggman sub-boss fought in the original version of this Zone from Sonic & Knuckles.
The boss begins with Dr. Eggman pressing a switch that plunges the player into the trash compactor, where the player is confronted by a ceiling-mounted device that reanimates damaged, Orbinaut-like badniks from the trash heap using electromagnetic energy. As it does so, the trash compactor steadily compresses the garbage the player is standing on, causing it to rise higher (making it easier to reach the device to damage it) but also leaving less room to maneuver; if the player takes too long dealing the 6 hits to defeat the boss, the compacted trash will eventually collapse under its own weight, instantly costing the player a life.
Knuckles will have to wait longer to be able to hit the boss due to his gimped jump, but it's possible to gain altitude by gliding into the reanimated badniks and potentially score early hits.