I am very much reminded of Omniscient Reader's Viewpoint.

One day, incorporeal black pyramids covered the skies of Earth. Six months later, there was an announcement from the pyramids: the Earth is online. Over the next three days, people are instructed to eliminate someone.

Tang Mo, a librarian, is pulled into a game, and so becomes an official player. He is granted an ability to mimic (a weakened version of) the special powers of others.

Besides Tang Mo, about 500 million people have survived the initial culling. Most are not official players, but 'reserve' players who eliminated someone in a game or otherwise impressed the pyramids, and a dangerous few are 'stowaways' who earned their place by killing someone during the three day period.