Super-successful game Fortnite may find its biggest business challenge yet as it moves to iPhone By: CNBC.com News March 17, 2018 at 07:56 AM EDT "Fortnite" is about to face a new challenge: The fickle world of mobile gaming. Read More >> Related Stocks: Activision Blizzard Glu Mobile Inc Gungho Online Entertainment Inc Zynga Inc Cl A