This is a Halo 5 Forge Map Feature. This is an Invasion Mini game made by WyvernZu called Infinity Siege. Think of it like Castle Wars and Halo Reach Invasion made a little love child. I've spent a good few hours trying to "destroy the enemy core". If you have Halo 5, this would be a fun custom to bring to your friday night, Let's plays. (The Link to the Map, and its Gametype, can be Found in the Video Description)