Korean Four-Character Idioms
용두사미
龍頭蛇尾
Word for word
“a dragon's head, a snake's tail”
What it means
A grand start that fizzles out.
When you'd use it
A drama with a great first episode and a weak ending.
Example
그 드라마는 용두사미로 끝났어.That drama started strong and fizzled out.