"Lead the Sentinels and Marines in search of the Index."
The Library: Evolved is a cut reimagining of the seventh mission in Halo SPV3. It is listed as SPV3C20_Evolved, also known as C20_Evolved.
Overview & Background
It seems this mission was inspired by Quarantine Zone from Halo 2. Details are sketchy but, apparently, the Master Chief was to team up with a group of Marines against the Flood and Covenant using a Sparrowhawk and a Mantis, from Halo 4, to break into the Library. Players would then have to fight through hordes of Flood and groups of Covenant to advance 2 floors and retrieve the Index, reminicent of the original Library. 343 Guilty Spark's role in the mission is unclear, but given the games narrative, it can be assumed he would have played a similar part as he did in the original version of the level.
The mission has been officially cancelled by CMT due to Marine versus Flood combat in SPV3 being deemed unfit for the modding team's vision of the level and functionality problems with the Mantis, which never even made it into the mod.
- From the level's description, it can be presumed that Marines would be present to assist the Master Chief. It is unknown if they would've been present from the start, dropped off by Pelicians, or have their own checkpoints just as the Covenant does.