“The Flashback Event will have three random mods from popular past leagues activated at once,” says the New Zealand studio. “The collection of mods will persist in that area for one hour and the collection of mods will vary from area to area. After an hour has passed the mods will randomize for each area again. Each area will also have the Bestiary league enabled which means that you can continue to finish your challenges while you compete in the Flashback Event. The possible league mods that you could see in an instance alongside Bestiary are Anarchy, Invasion, Breach, Ambush, Torment, Perandus, Beyond, Nemesis, Bloodlines, Abyss and Harbinger.”
And yes, the event is for both PC and Xbox One and will run four different difficulty modes (including standard solo self-found, where you can’t trade or group) starting May 4th through the 29th. Loot includes a special mystery box for hitting level 35, plus additional prizes based on level and rank at the end of the run.