343 Industries has been cagey about a Forge mode in Halo 4, but it would be shocking if the next numbered installment lacked the popular feature. As it turns out, the mode is in development from Certain Affinity, the studio behind Crimson Alliance and various Halo map packs.
Polygon reports that the studio announced it at the Rooster Teeth Expo. A few tweaks to the old Forge mode include the ability to lock items on the map so they won't be bumped, a cursor for selecting individual items, the ability to easily duplicate items, and a new lighting system.
In terms of tools that can be used to impact gameplay, you'll be able to set "Player Trait Zones." These can change parameters like run speed, jump height, or damage when inside a field on the map. Forge makers can also place a "Grav Volume," which shifts the gravity inside the field.