I started playing the original typing of the dead and it helped my typing alot and I became pretty fast, I still practised my typing and then when overkill came out on steam I naturally bought it and played through it on hard stage, I don't know if it was the difficultty but my typing seemed to get progressively worse with loads of errors because I was trying to go too fast without knowing what I was typing and it progressively made me slower because I was constantly using the backspace button. and when I completed it its still bad. My typing speed is fast but I always have to hit the backspace key because I am always making spelling errors