Starting today and until December 22, it is Gearsmas celebrations in Gears 5. During this period, you can unlock a Santa Claus version of Marcus Fenix, play the Horde mode Jingle Juvies and buy Christmas skins. There's also mentions of a return of Snowball fights. You can read more about all this over here and under the image is the description of how to unlock Father Gearsmas Marcus.
You can unlock Father Gearsmas Marcus for free just by completing the Gearsmas medal group:
• Making a List - Win 60 Versus Rounds, Horde Waves or Escape Acts
• Dashing Through the Snow - Complete 25 Rounds of Snowball Fight Versus Event or Jingle Juvies Horde Event
• Checking it Twice - Win 3 Matches of Jingle Juvies Horde Event or Snowball Fight Versus Event
• Jingle Hell - Get 50 Juvie Eliminations in the Jingle Juvies Horde Event
• Naughty or Nice - Get 30 Eliminations with the Snowshot in the Snowball Fight Versus Event
• One Horde Open Slay - Deal 200,000 damage in Versus, Horde or Escape