"But what’s cool is that you may be presented with three choices that span three different games. Say, Halo: CE’s “Wizard,” Halo 2’s “Lockout,” and Halo 3’s “The Pit.” Whichever gets the most votes is the game that MCC will launch, after which you’ll be taken back to the multiplayer lobby with your friends. Finally, the Extras menu is home to the Nightfall digital feature as well as the launch pad for December’s Halo 5: Guardians multiplayer beta. It will run from December 27, 2014, and end on January 22."
From IGN
http://www.ign.com/articles/2014/06/09/e3-2014-halo-the-master-chief-collection-halo-5-beta-announced-for-xbox-oneRegarding Halo 2
"Most multiplayer tricks and glitches should still work"
"Also, similar to Combat Evolved Anniversary, the original code is intentionally being left intact, so exploits and glitches like super jumping and BXR should still be possible in Halo 2 Anniversary."
Only bad thing is is seems like we probably won't have theater or forge which means no mlg maps on dedicated servers.
Watched an interview on ign with Frank O Connor after the reveal he said Halo 2 3 4 all have forge in the collection.