39.8 mpg is better than our 36 mpg rating of the Mirage here.
Diesel will never come to the States, but I see no reason for the ad being fake. It's been stated by other sources that a diesel Mirage may be made for some markets.
Quote - "Under the hood, Mitsubishi could be considering a wide range of powertrain options for the Mirage. Globally, we could see engines like a turbocharged 0.9-, 1.2-, 1.5-, or 1.6-liter. While not expected in the United States, there will likely be a diesel variant as well that comes with a 1.5-liter diesel engine. Industry experts also expect to see an all-electric version, though that model may come out a bit later."
Taken from
https://donrobinsonmitsubishi.com/20...ht-St-Cloud-MN