This pack comes from the Humble Bundle December 2018:
https://www.humblebundle.com/monthly/p/december_2018_monthly

To the best of my knowledge, the two Steam keys cover (1) the game + DLCs, and (2) prequel, as Humble Bundle stated on their website:
"METAL GEAR SOLID V: THE DEFINITIVE EXPERIENCE is the ultimate collection of the METAL GEAR SOLID V story. Includes the critically acclaimed METAL GEAR SOLID V: THE PHANTOM PAIN and its prologue METAL GEAR SOLID V: GROUND ZEROES, as well as all their DLC contents."

As SteamGifts doesn't seem (to me) to support adding two keys for a single winner, I will send the second key (prequel) once a winner is drawn, via email.

Good luck! :D