How do you beat mission 6 in sniper assassin 3

You should press F to make his fear go up. When the lamp stops swinging, press F again. In the meantime, pressing W or Q will keep his fear from going down, while hitting S increases it (but can kill him if overused). You can use D intermittently with W and Q. When Fear is higher than Guts, press the spacebar.

(see related question)