Halo Infinite's forge mode is extremely technical and gives players more control over custom games and parameters than ever before.
Based on new leaked info it's easy to see why Halo Infinite's forge mode was delayed. The reality is the new forge is almost like a mini games engine complete with its own scripts and nodes. It's more like Battlefield 2042's Portal mode--or maybe something like a basic Unreal Engine or even Bethesda's Creation Kit modding tools--than the forge modes in previous Halo games.
Halo Infinite's forge will let users control everything in the game, including weapon, vehicle, and character respawns, placements, events, bots--you name it. There's even options to tweak biomes, build customized structures with Infinite's assets. Conditions can be set--e.g. x event happens when you enter a specific vehicle or cross a doorway threshold--and also options for highly technical editing via vectors and math-based trigonometry.
If it's in the game, forge can edit and adjust it. Infinite should have the best custom games as a result and we should see some truly crazy and memorable builds.
It's unknown whether or not this detailed forge editor is exclusive to PC or not. Remember that Xbox Series X/S and Xbox One owners can technically use mouse and keyboard in Halo Infinite so it's possible the tools will be included on console too.
Forge won't be out until 6 months after Halo Infinite's launch, so expect it mid-2022.