It's different from the song game! In this one, one person posts the chorus of a song and the other person re-writes the lyrics in a funny and creative way. Remember when teachers would tell you to quote something but in your own words; that's what this is.
You can translate the chorus into Shakespeare, you can turn it into a rap, you can use old English, and so on. You can also simply take the lyrics and make all of the lyrics opposites or synonyms.
Run it through a site like this link if you have to lol.

It doesn't necessarily have to be the chorus either--it can be any verse you'd like.

Example;

User 1: Open up your eyes save yourself from fading away now, don't let it go. From Within Temptation's Heart Of Everything

User 2: Give me a break - open up your eyes save yourself from fading away now, don't let it go. I've been unfairly treated by the press

Sing me a song of your beauty of your kingdom. From Nightwish's Angels Fall First