IWHBYD Skull (Halo 3)
From Halopedia, the Halo wiki
Were you looking for the Halo 2 version of the IWHBYD Skull?
The Halo 3 IWHBYD (I Would Have Been Your Daddy) Skull is located on the campaign level The Covenant. This skull has no actual gameplay effects, but reverses the frequency of the dialogue spoken by non-playable characters, allowing several humorous lines to be heard where otherwise such humorous lines would be very rare.
The name of the skull is based on a statement, occasionally uttered by both Sergeant Johnson and Sergeant Stacker in Halo: Combat Evolved: "I would have been your daddy, but a dog beat me over the fence!" The quote was originally spoken by Pete Stacker.
It is also the name of the first chapter of the campaign level Assault on the Control Room in Halo: Combat Evolved. Not only is the skull's name a reference to this line, but the skull's description reads "But a dog beat me over the fence" The exception of this is in Halo 3: ODST and Halo 4, where the description reads, "Rare dialog is common and vice versa".
When you reach the final scene, where the Prophet of Truth is planning on lighting the seven rings, proceed as you would normally: kill the Covenant, kill Truth, and kill the Flood, but do not jump down the elevator shaft once you have finished that.
Once the bridge is devoid of enemies, you will have to jump through the seven holograms of the Halos in a specific order.
You should jump through the rings after Truth dies. The skull will still appear if you are playing in co-op (2-4 players).
Note: you can restart jumping through the rings without restarting the level over as long as you start from the beginning.
Once you have completed the sequence, the skull will appear at the beginning of the light bridge leading to Truth's podium. If you are not sure you got it, then look at the rings when you complete the sequence; they will be blinking in sequence. The Halo theme will play as you get the skull. You must then finish the level, or the skull will not be saved to your profile and you will have to do it all over again.
The IWHBYD Skull causes rare dialogue in the game to become commonplace, and normally frequent dialogue to become rare. These lines are can be heard spoken by all talking non-player characters; both enemies and allies.
For example, if a Jiralhanae is killed, one of the surviving Brutes might say, "He was my lover!" or "Every pack-brother for himself!" These lines can be heard without the skull on, but it becomes much more likely to be spoken with it on.