666 means "yo yo yo", which is a buzzword on the Internet nowadays. It is often used when playing games, and it means that you are very good.

It first originated from YY’s LOL anchor Ai Loli, and then became popular on YY and gradually became popular on other live broadcast platforms and the Internet. It is a simplified language for numbers that has become popular in LOL games. 666 is the homophonic number of the spoken word "Liu", and has the same relationship as the homophonic number of the written word "I", which is 5.