There is only one file type that uses the .SC2MOD extension:
Blizzard StarCraft 2 Modification File
Modification archive used by StarCraft II: Wings of Liberty, a real-time strategy game where players battle as the Protoss, Terran, and Zerg races; contains information that changes the properties of gameplay; created in Blizzard's proprietary Mo'PaQ format (.MPQ files).
SC2MOD files can be created with the StarCraft II Editor (also called the "Galaxy Editor"), which is included with the StarCraft II game. They can be used to modify map properties, such as unit capabilities, triggers, text translation, and computer artificial intelligence.
NOTE: Since SC2MOD files are saved in an MPQ format, they can be renamed with the ".mpq" extension and opened with an MPQ editor.
Updated: January 28, 2011