From Press Release:
Wield true power — the Infinity Gauntlet! Hop into Fortnite Battle Royale and become Thanos in the Infinity Gauntlet Limited Time Mashup, available now for free on all platforms that Fortnite is available.
Players will drop in solo as they hunt for and fight over the Infinity Gauntlet. The first to equip the Gauntlet will transform into the mighty Thanos and wield the Gauntlet’s power!