Today the game mode 'Invasion' was released for play in the H : R beta, and I've played a few rounds.
It's 6 vs. 6, Spartans vs. Elites.
Elites will attack two generators.
After they're destroyed, two more will open up.
As of now, more load outs are available for use. On this stage, if you spawn in front of the first generator, there will be 2 Sniper Rifles, 2 Rocket Launchers, a Spartan Laser, and a Designated Marksman Rifle.
After both areas on this stage are taken down, a large core will be released from it's hold. The Elites must pick it up, carry it outside and across the map to a Phantom waiting outside that will take it for a clean getaway.
I'm going to say right now that the Elites have an EXTREME handicap over the Spartans.
Elites move faster, have better armor, and their health regenerates contrary as to were the Spartans must pick up a med kit. In invasion slayer they get vehicles faster, as well.