Halo 3
Halo 3's story mode contains nine levels. It finishes the story of the Halo trilogy. The story can be played alone, with a friend on the same console or with four players over Xbox Live. The first player takes control of Master Chief, the second player plays as the leader of the Elites, Arbiter and the last two as elites themselves. There are skulls hidden through the levels. If they are found by any of the players the gameplay changes in some way. For example one skull makes confetti and balloons appear when a player gets a headshot and another makes all enemies stronger and tougher.