Unknowns are basically moving scrapheaps made out of the machines in the Russian army powered by a central red core, when the red core is knocked out it runs around quickly on it's own two legs while the scrap is magnetically pulled towards it. It can move on ceilings, walls, anywhere really. Can raise the section with the core in it and emit a random bunch of laser lines around, can raise multiple arms with guns on the end and also just grab and kill you. The only way to defeat it is to destroy the core. Can fit through certain vents.
Gameplay notes (Quoted from this video):""One of my favourite enemies of the game, it has that "cute, yet deadly" vibe that I like on dangerous enemies. It's weak point is it's core, which is not always exposed, but sometimes he does the "christmas tree" stance, giving you a good chance to shoot the hell out of it with the HMG. Of course you can weaken it, by blasting a few Shotgun shot on it. Soon the surrounding scrap will fall down, giving you another chance. But careful, if it "blooms", and the core is flashing for a second, it means it's about to perform it's "fatality" move, which is quite... painful, even to watch."