There are some in Halo 3 ODST.
One on Heretic, one on Longshore and one on Citadel.
These maps are the new mythic map pack.
you can get all of the skulls on multiplayer. =)
if you want to know where the skulls are all you have to do is go to youtube and put in "halo 3 odst mythic skulls" and it will show you how to get to them
ok, go to youtube and type in "how to find all halo 3 skulls" then watch the video and get the skulls. yes, its that simple.
By getting skulls.
get all skulls
Find them your self
Go to Halopedian.com. They have the largest source of everything Halo.
If i am correct then it is the same as the skulls being off.
archon armor
THey get you an achievement, and they get you the Hayabusa helmet.
All skulls are automatically unlocked for Halo 3: ODST due to gameplay reasons.
Sorry there arn't any, The only skulls are in "Halo 3" Which are used in "Halo 3 O.D.S.T."