The meaning of 666

In terms of Chinese, 666 is an internet slang that means something along the lines of "good job", "well done".

In most parts of China, “溜”, pronounced "liu", means "good at doing something", and the number 6 is also pronounced "liu" in Chinese, and that's how it came about.

This slang was first used in online games, likely MMORPG games, before it became widely used. Which is logical when you think on it, as those who do play online games would know that typing fast often saves lives. Typing "666" is definitely faster than typing the same in Chinese using the QWERTY keyboard - imagine wasting time choosing the correct word in the midst of battle!

Increasing the number of sixes, I guess, would mean deepening the degree of the praise, similar to "!" versus "!!!!".