As the units gain honor, more units can be summoned via drop pods. Predator units can only gain resources by killing opponents, which is granted via an 'honor' system. Marine units are entirely medium to long range fighters and have support units to perform specific actions that aren't available to humans like other species (such as healing). These credits can be spent on upgrading existing units or calling in new ones via dropship, which drop units off at specific landing beacons. Human units, appearing in the game as the US Colonial Marines, gain credits by killing enemies and repairing atmospheric processors. The population cost of units varies drastically between species. Each species has a population cap that varies by level. Starting conditions are often dependent on story developments. Players must move through specific objectives in order to advance a level, ranging from killing certain enemies or performing tasks like repairing an object. Each species has a single resource that is used to summon or upgrade units, and methods of unit generation differ radically. Aliens Versus Predator: Extinction is a real-time strategy game with a focus on unit management over base-building and resource gathering.
