I Would Have Been Your Daddy Skull

Skull Effect:

Unlocks hidden dialogue throughout Halo 3’s campaign.

Campaign Scoring Multiplier: None

Skull Location:

The IWHBYD Skull is located at the end of the seventh level, The Covenant.

The Skull is located in the large hallway with the 7 Ring Holograms and the Prophet of Truth. First fight your way through the hallway and kill the Prophet of Truth as you normally would to complete the level.

After you have killed Truth, head back through the hallway and kill all of the Flood but don't jump down the hole you normally would to complete the level. Instead, you have to go back into the hallway and jump through the Halo Ring Holograms in a specific order to make the Skull appear.

That order is as follows (1 being by the entrance, 7 being by the bridge to Truth):
4 6 5 4 5 3 4

To help coordinate the jumping through the rings, the ring with the red sections in it is ring 4.

When you jump through the final halo, the rings will start lighting up in a linear fashion. The Skull will have appeared on the bridge to Truth where the control panel for the bridge used to be. When you grab the skull, all of the rings will start playing the main Halo Theme Song.