Microsoft today announced which two Xbox One games and which two Xbox 360 games will be made available to Gold members free for the month of May.
For the entire month, CastleStorm: Definitive Edition on Xbox One will be available to download for free. Pool Nation FX is also carrying over from this month (April) through the entirety of May.
On the Xbox 360 side, Mafia II will be available for free from May 1 through May 15. On May 16, F1 2013 switches places with Mafia II for the remainder of the month.
Presently, Child of Light and Pool Nation FX are both available free for Xbox Gold members on Xbox One, and Assassin’s Creed: Black Flag and Army of Two: The Devil’s Cartel are still up on Xbox 360.
Source: Major Nelson blog