P factor - Descending blade has a greater angle of attack and thus creates more thrust then the ascending blade - especially at high (wing) angles of attack. Thus with a standard clockwise (from cockpit) rotating (right-turning) prop you tend to get a left yawing tendency in the climb.
P maybe stands for Propellor, I'm not sure.
Critical engine - That engine which if fails will cause the most adverse reduction in controllability. On a standard twin it will be the left engine, on counter-rotating twins (PA34/PA44 etc.) there is no critical engine.
Tristadecaphobia - not a clue.
Hope this helps a bit.