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

: The update adds Christmas-themed game menus, holiday music by Anna Lazarev and Ivan Špeljak Jitz, and festive enemy variants, such as Sirian Werebulls with glowing red noses and bosses dressed as Santa Claus.

: 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) Serious.Sam.Siberian.Mayhem.Merry.Christmas.v1....

If you were specifically looking for features from the update (which arrived earlier in August 2022), it added: Guide :: Christmas event: XPMR "Freezer" Raygun weapon skin : The update adds Christmas-themed game menus, holiday

A "solid feature" of the (Patch 1.06) for Serious Sam: Siberian Mayhem is the permanent unlock for the Christmas Event via a new New Game+ perk . Key Christmas Features Key Christmas Features