His megalomaniacal plans eventually plunged the company into financial crisis.

megalomaniacal 是由词根 megalo-（表示"巨大的"）和 mania（"狂热、痴迷"）加上形容词后缀 -acal 组成的复合形容词。megalomania 原指"夸大妄想症"，megalomaniacal 形容人"妄自尊大的、极度自负的"，带有贬义色彩。