yeah, ren shan ren hai is a pretty good one, and it’s also probably one of the more frequently used ones.

Mandarin Chinese:

I thought of a couple involving animals.

沉鱼落雁 (chén yú luò yàn) - literally “sinking fish and grounding geese” - describes a beautiful woman.

虎头蛇尾 (hǔ tóu shé wěi) - literally “having the head of a tiger and the tail of a snake” - meaning: 1. having a strong start and a weak finish. 2. describing someone who is treacherous and doesn’t do what they say they will.

Lots of idioms in Chinese are “chengyu” consisting of four characters.