Age of Empires Online: Skirmish Booster Pack

Create your own battle! Fully configurable Skirmish Hall allows you to choose every element of gameplay, from resources, teams, and victory conditions to opponent civilizations, difficulty, and strategy. All units are automatically unlocked and battle-ready! Play with up to 3 friends against up to 4 enemies, or battle against civilization-based computer opponents on more than 20 different battlegrounds to earn new advisors, vanity trophies, and gear. YOU control the battlefield!

Source: Steam Store Description