Challenge mode will present players will three different levels of challenges, linked to achievements, that test different gameplay mechanics that aren't necessarily used in the campaign. The units in this mode are the same used in multiplayer. Each challenge has three award levels: bronze, silver, and gold.
I was able to try two of them earlier this week. The first tasked me with killing wave after wave of enemy units with a limited force of High Templar and Sentries, two Protoss spell-casting units. Using the various spells and abilities, I attempt to survive wave after wave.
It's definitely a challenge and I was not able to hit the gold level even after five attempts. To succeed, you'll need to use all of the spells across both units and morph the Templar into Archon's when they run out of mana. It requires intense micromanagement skills.
The second challenge presented me with five sets of Protoss units and five sets of enemies arranged in a pattern around a map. The goal is to kill as many units as possible in a few minutes. This requires managing all five forces simultaneously, using the abilities of the units in question to advance.
What makes this an "Elite" challenge? It doesn't allow the player to click spell or command icons. Hotkeys must be used to get spells and abilities to work. The mouse is still used to right-click to issue orders and selection units, though.
After a few tries, I was able to hit the gold level of this challenge, but it helps develop micro abilities as well as offer some great practice for multitasking. Thankfully, it can be practiced over and over again with the same conditions.
The challenges should help teach skills like rush defense, multitasking, macromanagement, and micromanagement all from the saftey of an offline, private experience. The map editor will even allow community members to build new challenges, though they will not be tied to achievements.
StarCraft 2 is currently in closed beta and Blizzard is targetting a mid-year release for PC and Mac.