ODST has Halo 3's multiplayer portion?

[RaveRaze]

I heard that if I buy ODST I get Halo 3's Multiplayer as well is that true

 

[NeutralMunchHotel]

Yes. Yes it is.

I'm not sure if achievements and maps are usable on each other, but I hope so.

 

[Kermi]

There's a seperate disc (Halo: Mythic) that includes Halo 3's multiplayer and every map - the 11 original plus the 13 DLC maps. I believe any Halo 3 multiplayer achievements you don't yet have will be unlockable via this disc (since the Vidmaster: Brainpan achievement and the map-specific achievements like getting a shotgun spree on Longshore and a Sword Spreee on Citadel are Halo 3 achievements, not ODST achievements.