Blood gulch maps are modded versions of the game's instant favorite and classic map. some of the bloodgulch mods include things like automatic rockets, modded weapons like M4s and m249 SAWS; and also weapons from halo 2 or halo 3. Some very famous ones were cmt_coalgation which included dual-wielding abilities and the SPARTAN LASER cannon. others were addons or replacements like PELICAN WARS which added a pelican dropship to the middle of the map. probably the best was plasma gulch or THE MATRIX MOD. most of the time it'd be a new mod with new name, and sometimes you would have to make backup copies of the orginal game's map.