In the game, the player fights enemies using weapons and plasmids (powers that the player gets from gathering ADAM). Each weapon (except for the wrench) has three different kinds of ammunition with different effects. The special ammunition is more powerful against certain kinds of enemies, but they are more expensive and hard to find. Including shooting lighting bolts, shooting fire, and lifting objects without touching them. Some plasmids are found in the game world, but most must be bought and upgraded at special vending machines. The player gets ADAM by harvesting or rescuing Little Sisters, but before the player can do that, the player must kill the Big Daddies protecting them. Big Daddies are hard to kill and they can kill the player quickly, but most Big Daddies will never attack the player unless the player attacks them first. The player can use this to plan and prepare their attack. After the Big Daddy is killed, its Little Sister will come to check on the Big Daddy. At this point, the player can either harvest or rescue the Little Sister. Harvesting the Little Sister will give the player more ADAM and the player can therefore buy more plasmids, skills, and upgrades. However, if the player harvests too many Little Sisters, the player will get one of the bad endings. If the player rescues Little Sisters, the player will get less ADAM, but will get other rewards if the player rescues a certain number of Little Sisters.