noun
anticlimax; strong start, weak finish
A yojijukugo describing something that begins impressively but ends poorly or fizzles out. Often used for projects, stories, or events.
あの映画は竜頭蛇尾で、前半は面白かったのに後半は退屈だった。
That movie was an anticlimax; the first half was interesting but the second half was boring.
彼の計画は竜頭蛇尾に終わった。
His plan ended with a strong beginning and weak finish.