For the first time in a while, a Diablo 4 season won't just be about fancy new powers for your build. In season 10, or the Season of Infernal Chaos, the best loot in the game can drop as "Chaos armor", allowing you to use items in ways you never could before.
Several Unique items and their powerful guaranteed stats will have new Chaos variants that are even more powerful than normal and can be equipped in new slots on your character. The idea is that a Unique that could only drop as gloves before can now show up as a pair of boots or some other piece, which opens up all kinds of combinations and new builds.
