It makes the environment have slightly darker colors. Returning from Halo 3 are Forge filters, VFX overlays that help change a map's appearance.
Many of these objects are based on existing setpieces of Halo multiplayer maps, with players able to place down the bases seen on Blood Gulch or the components that make up Ascension, among others.
For example, up to 50 Wall objects can be placed, but this can be any combination of 50 objects within that category as opposed to a set amount of individual objects. two Scorpions per map in Halo 3 now upped to eight Scorpions per map)
All weapons can now be placed on all maps.
