The Little Sisters roaming the levels are still crucial for accessing Adam, but now players have a choice: they can adopt them and protect them from harm, or harvest them themselves. Harvesting a Little Sister requires the player to fend off splicers while it searches for Adam-infused bodies. Once the task is complete, the player can choose to keep the Little Sister as their own or free her.
BioShock 2 also features multiplayer for up to 10 players, developed independently from the single-player campaign. Players can compete in various modes such as Deathmatch, Team-Deathmatch, Capture the Sister, and Adam Grab, while earning ranks and unlocking additional radio messages that advance the story behind the civil war in Rapture.