One of those, Robot Entertainment, has been working with Microsoft to develop "additional content" for the Xbox 360 strategy game.

Now, Microsoft has revealed the first details on that additional content in the form of the "Strategic Options" downloadable add-on that's due out in the "coming weeks."

The as-yet-unpriced download will bring three new multiplayer modes--Keepaway, Tug of War, and Reinforcement--to the game, along with four new achievements.

Keepaway Mode is the "Halo Wars" adaptation of Capture the Flag. Teams will battle it out to capture a free-roaming Forerunner Sentinel to score points before the other team. Capture three sentinels to claim victory.

Tug of War Mode is all about having a stronger army than the opponent. Defeating enemies is essential, but success is determined by a combination of the army, buildings and resources left standing in the end.

In Reinforcement Mode, all active battle units are provided in successive waves. Players must adapt their tactics and use the ever-changing set of units to outwit and outlast the enemy.

As for the new achievements, a total of 100 points will be available:

• "One and Done" (30 points): Score the winning point in a game of Keepaway against Legendary A.I.'s
• "Pull Hard, Pull Deep" (20 points): Win and never trail in a Tug of War game
• "Freak on a Streak" (20 points): Gain at least 15 population from a single wave in a Reinforcement game
• "Living Loving Bug" (30 points): Obtain a Scarab during a Reinforcement game