Strategy to beat it[]
Shadow Rat's "Shadow Challenge" is by far the hardest night to beat in the entire game, and rightfully so, however it isn't that combat against him is difficult. The difficulty comes in with Shadow Rat's speed. Shadow Rat is the fastest enemy in the game, from going from door-to-door, to moving his head in combat, to going under the bed and popping back up, and even returning after combat is over. Don't expect to ever have a second without combat in this challenge; you'll be fighting more than you'll be resting. That being said, here's a few tricks you can use to get an edge on Shadow Rat:
-Shadow Rat moves the fastest in the game, but as long as you can master Monster RAT's triangular movement cycle when in combat, then Shadow Rat will be easy enough, as long as you have fast reflexes to boot.
-Shadow Rat moves instantly to another door when you shine a light on them. To help keep them at bay for long periods of time, continuously shine your light between the "hallway and dresser," or the "closet and dresser." This way you'll have two of the three locations constantly checked, with the third location saved for if Shadow Rat is in neither of the two locations. The best spot for this is the "closet and dresser," because hitting Shadow Rat by the hallway door when in combat is easier than either of the other two locations.
-Either keep tending to the tape recorder if you're skilled and fast enough to do so, or completely abandon it. Not only can Shadow Rat distort the tape recorder while under the bed, making hearing his movements to quickly shine your light on them more difficult, but it's also very risky since Shadow Rat moves so quickly. Choose your poison, and stick to it.
-The trickiest part to beating Shadow Rat is shining your flashlight on their face when they pop out of the bed. You have literally two seconds to shine on their face. Any more than that, and Shadow Rat will attack you. Try practicing how fast and precise you can do this process on Night 5 as practice, and once you feel confident enough, try, try again! This isn't really necessary, though, if you're already skilled at doing the motion.