Serious.sam.siberian.mayhem.merry.christmas.v1....

The Merry Christmas Update 1.06 introduced several holiday-themed and gameplay enhancements:

: A unique cosmetic for the XPMR "Burner" Raygun, unlockable by finding a Christmas Tree and completing a special portal challenge on each of the game's five levels. Serious.Sam.Siberian.Mayhem.Merry.Christmas.v1....

: Introduced alongside the holiday content, this mode allows you to restart the campaign with all your weapons, skills, and gadgets while introducing tougher enemy spawns and weapon upgrades. Related Gameplay Improvements (v1.0.4) The Merry Christmas Update 1