All of these are set before the events in the novel, so they don’t contain any spoilers. They also focus on three of the characters who don’t get so much “screen time” in the novel itself: Seth, Kay and Edwin play larger roles.
(They’re stand-alone, but if you want them chronologically, read them in the order below.)
Robert joins Lycopolis, staying as anonymous as possible.
Hannah and Kay form an in-game alliance.
Mark has a life-changing conversation with Seth.