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Either avoid it, or lead it to the mirrors. You can kill him by breaking a mirror while he's reflected in it. Don't stick yourself to the gate if possible: for some reason his hitbox is a bit bigger than the gate's. 

The sound should also tell you it's current approximative position (the audio listener is on the character itself, not the camera).

Thanks for playing!

Edit: there's also a cheat code to skip a level when you're stuck: NumPad9.