Hero decides to move twice and acquires 8 movement points and has 4 fatigue currently. After spending his 8th movement point, the overlord plays pit trap, and the hero fails the test. Is the hero stunned or can he, after testing, spend a fatigue to gain an additional movement point to pay the cost? Thanks in advance.

I don't have the card in front of me, but my impression when I read it was definitely that you cannot suffer fatigue to gain movement points after the card is played (until it has been fully resolved). You need to save up movement points in advance if you want to forestall it.

beta said:

Spending a fatigue to gain a movement does not interrupt an action. So, the Pit Trap card would need to finish before you could spend the fatigue. So it wouldn't help you.