Halo 3: Mythic is the Halo 3 multiplayer disc that comes with Halo 3: ODST. The disc includes Halo 3's multiplayer component, Forge, the Theater, and every Halo 3 multiplayer map, including three new maps: Heretic, Citadel, and Longshore, along with their respective achievements.
- Getting Halo 3: ODST is more cost efficient than buying all of the map packs individually, as you get the game with all of them.
- The armor customization screen in Halo 3: Mythic is a graphically updated version of its Halo 3 counterpart, including dents in armor, bullet holes in armor, and a darker visor.
- The background scenes in every game mode menu is different in comparison to Halo 3's.
- Two new demos showcasing the Mythic map pack and Cold Storage play when idle in the main menu.
- In the Custom Games lobby, scrolling through individual gamertags will make the Elite in the background's shoulder emblem change to same as that person's emblem.
- Citadel, Heretic, and Longshore are now available through the Mythic II map pack on Xbox LIVE Marketplace for the equivalent to 800 Microsoft Points ($9.99 USD) in the user's currency.
- Despite being a multiplayer disc, Mythic does have an accessible Campaign lobby, but it is only viewable on Xbox LIVE if one player has the campaign disc and switches to the Campaign lobby, though the user on Mythic would not be able to play.
- In the Forge Lobby, a monitor is seen in Citadel projecting a beam of light.