PROTIP: Save yourself a couple bucks and buy ODST from your local game store for $7-10. You also won’t have to install all that DLC onto your hard drive, thus saving space. MAKE SURE THOUGH that the copy of ODST that you buy has the Mythic Disc in it before the sale is finalized. I’ve seen one store sell the game (which was brand new or practically brand new) without it.
Good advice, I would also like to add a little more information for those of you who go on the marketplace and see ODST on Games on Demand.
Do NOT purchase the GoD version of ODST, you are purchasing only the campaign and Firefight that ODST offers, the map packs are not included with the GoD purchase. 
> Do NOT purchase the GoD version of ODST, you are purchasing only the campaign and Firefight that ODST offers, the map packs are not included with the GoD purchase.
Also this. GoD version of ODST is kind of a rip off honestly. But then, if the Mythic Disc content was sold alongside it, it would probably devalue the individual map packs themselves.
Good advice. Plus ODST was an awesome game anyway. Well worth the money for it along with the Mythic Disc.
Hang on, so if i install disc 2 of ODST, I then have the Halo 3 DLC??
I’ve gone through about 4 different consoles since i last played ODST or 3 and all my Halo 3 DLC was bought on a now defunct Live account, so i have no Halo 3 DLC to re-install so to speak!!
> Hang on, so if i install disc 2 of ODST, I then have the Halo 3 DLC??
>
> I’ve gone through about 4 different consoles since i last played ODST or 3 and all my Halo 3 DLC was bought on a now defunct Live account, so i have no Halo 3 DLC to re-install so to speak!!
Disc 2 is the entire Halo 3 mp experience and it comes with all the maps. So if you have that disc you pop it in your Xbox and play Halo 3 from it, no need to install anything to your HDD.
I have the disc, but can i not just install it and still have the dlc maps rather than using the physical disc??
Good advice. Also, DO NOT INSTALL HALO 3 CAMPAIGN TO YOUR HD FROM THE DISC. It causes severe load time increases, so don’t do that. Also, it doesn’t even let you install the MP disc to the HD.
> I have the disc, but can i not just install it and still have the dlc maps rather than using the physical disc??
No. If you install it to the hard drive you will still need to load the disc at first to play it. This is a simple way to prevent video game piracy, as installing the game to your hard drive doesn’t actually install all the data. For example, I already installed Halo 3 to my hard drive from the original disc, which it said took up 3.3GB of space. But the actually Halo 3 download from XBL marketplace is 5.7GB. As you can see its a big difference. This is why games installed from disc still need the disc to actually load up, again this is to counter piracy .
Also installing the ODST mythic disc, then trying to play from the original Halo 3 disc wont let you play the DLC either, since both discs are classed as two separate games and the DLC maps are on the Mythic disc not the campaign disc.