Complex sentence: In February 2011, he released his first major project, his second mixtape "Nostalgia, Ultra", which produced two singles: "Novacane" and "Swim Good".
Split into simpler sentences: In February 2011, he released his first major project, which is his second mixtape "Nostalgia, Ultra". The mixtape spawned two singles: "Novacane" and "Swim Good".