Gametype is "Invasion: Starfall", or you can use regular invasion and switch the attackers to Spartans.
Download the map from my file Share
Welcome to Starfall.
Starfall is an Elite defense invasion map with a very specific theme and experimental gameplay dynamics...
Ever since I discovered the IWHBYD skull in Halo 3, I've been playing each and every campaign with it on. Someone made a neat video showing off the funniest lines that NPCs can spout out. It's two parts funny, one part nostalgia. Enjoy!