From Wikipedia
Spore: Galactic Adventures is the first expansion pack for the multi-genre game Spore. The main feature added to the game is the Adventure Creator. This Creator allows players to create various missions, which are then populated into the Space stage in a manner similar to the other content created in the original game. Players add elements to the adventure by dragging them from a menu and dropping them into the world. Creatures, vehicles and buildings created using the game's other editors can be selected and placed throughout the world. The player can also set creatures' behaviours from aggressive to friendly, and add speech bubbles. In addition, fixed objects from the previous stages of Spore, as well as game play objects, such as bombs or teleports, can be added to the game. Players can select a range of special effects and drop them into the level. Sounds can be added to the game in the same manner, although new sound files cannot be added to the game. A complexity meter exists to prevent too many objects being dropped into the game.