Some more interesting changes coming to StarCraft 2 with the latest patch than the usual balance changes and fixes.
StarCraft 2: Legacy of the Void patch 3.3 adds mutators and mastery levels
StarCraft 2: Legacy of the Void gets a shakeup with the latest title update. Two new features will be added to co-op missions: mutators and mastery levels.
Mastery levels are a prestige system. There are nine levels available, and any XP earned on a maxed-out commander will contribute to your total. Each level unlocks one point to spend on strengthening units and abilities. These bonuses are then persistent across all commanders.
Mutators are optional complicating factors available in any co-op missions. Examples include a chance for worker units to fall asleep, or attack by invisible forces. Each week, Blizzard will combine several mutators into a Mutator Challenge event you can tackle with a pal.
One example of a Mutator Challenge is called Train of the Dead and is played on Oblivion Express; waves of infested will constantly assault base defences, infested units will rise to replace any enemy you kill, and the fog of war will be replaced by darkness.
Another example is Time Lock, played on Local and Load. Enemy units will move twice as fast, and will use Time Warp on your units to slow you down. Slowing down may be a good idea though, as there'll also be mag mines everywhere.
Blizzard has asked players to share their ideas for future mutators and mutator challenges.