From The TimeSplitters Wiki

The Machinist's Robot is the boss of the Robot Factory level in TimeSplitters 2. It's only fair that the most annoying/long level of the game has the toughest boss of the game. Still, it's not that hard. After destroying the power node, you enter the last room. It has some doors on each side and a white box that The Machinist is in. That is the Machinist's Robot, and he is controlling it. It has four arms appended with razors and screwdrivers that will swipe at you. To defeat him, in easy and normal mode, use the ElectroTool. In hard mode, the toughest part of this will be the ChassisBot that comes to life on each side with the Plasma Autorifle. After killing them, launch all your plasma grenades on top of the middle of the Machinist's Robot, and he should be gone in no time. The Time Crystal in the level is on the upper floor behind the Machinist's Robot.