Solution is Lion, Leafy Branch, Bird.
He cannot enter the S.T.A.R.S. Office, the Save Rooms (usually), or the Clock Tower. Solution is Lion, Leafy Branch, Bird
The final stretch requires you to create a herbicide to kill Plant 43. Solution is Lion
Use the combat knife as a defensive item only when grabbed to avoid taking damage. the Save Rooms (usually)
Use wooden boards on the ground floor windows early in the game to prevent "infinite" zombie spawns.
He reacts to sound. If you run or fire weapons, he will find you faster.
Once you extinguish the fire on the helicopter wreckage, Mr. X will begin stalking you.