After watching three hours of comedy, the audience became saddened with jokes.

saddened 是动词 sadden 的过去分词形式。sadden 由形容词 sad（悲伤的）加上动词后缀 -en 构成，表示"使变得悲伤"。在句中作表语，表示观众"变得悲伤"的状态。