Grunt Birthday Party is a silver skull found in every Halo game to include skulls, excluding Halo: Spartan Assault and Halo: Spartan Strike. Being a silver skull, it affects gameplay minimally when activated, although can be used for offensive purposes in some games, such as Halo 3: ODST.
On the level The Arbiter, you should fly down as soon as you get to the first Banshee in the level. Below you is a large beam-like structure (not to be confused with the one directly below you that turns and goes vertical) running from the arm of the station you just came out of to one exactly like it on the side opposite. Below this structure are three cylinders hanging down, with cylinders of light shooting out of the bottom (and the sides). They look like they are what keep the station afloat. If this explanation is too vague, they are the absolute lowest parts of the station. Now go to the middle engine and land on the top part of it. This and the other engines connect to the large structure mentioned earlier. The tops of the engines come up to meet the structure at an angle, where this angle is under the connecting structure and coming up to meet it, there is a place to walk (like being under a bridge). Under one side you will see the six Heretic Grunts dancing in a circle around the Skull.
- On your way to the barracks, you will come across a section in the level where you are required to drop down into a shaft. At the bottom are several pipe entrances where Drones fly out of. Reaching the bottom will initiate a Cortana Moment.
- Before you drop down, at the end of the corridor, there is another large drop (purple pipe with a rotating fan). Look down at the drop and you will notice a small ledge protruding out a little bit with a green arrow in the middle.
- Approach the edge very slowly, and as soon as you drop, start moving backwards. You should land on the ledge.
- The skull will be located at the end of this passage.
- After the battle with the Chieftain and Brutes, grab a Gravity Lift.
- Continue on until you are in the shaft with the Drones.
- Walk down the corridor and go down the large drop.
- Turn around and throw the Gravity Lift. Try to lay the lift as near to the pipe as possible. Laying it in the middle won't always work.
- Go through it and you'll enter the passage with the skull at the end.
Halo 5: GuardiansEdit
The skull can be found on the level Enemy Lines. After slightly veering off a path, a lone Unggoy can be found sitting alone on a ledge, singing, and holding the skull in his hand. Killing this Unggoy will allow the player to pick up the skull.
Somewhat dissimilar to its later appearances, the Halo 2 Grunt Birthday Party skull causes a Plasma Grenade explosion to occur at the impact point of any critical hit, essentially meaning headshots (or shots on the infection form embedded in a combat form's chest, in the Flood's case) cause the target to explode.
Halo 3 and Halo 3: ODSTEdit
In Halo 3 and Halo 3: ODST, the effect is the same as in Halo 2, except that it occurs exclusively on Grunts, and the explosion is retextured as a spray of confetti, with the additional sound of children cheering.
Halo Wars' version of the skull creates a confetti effect upon the death of any and all Grunts, whether they were killed by a shot to the head or not.
Halo: Reach, Halo: CEA, Halo 4, Halo 2: Anniversary and Halo 5: GuardiansEdit
In all since appearances, the skull has the same effect: it creates an explosion of confetti around the head of any Grunt killed with a headshot. However, this is purely an aesthetic effect, as the explosion no longer damages nearby enemies. In the cases of Halo: Combat Evolved Anniversary and Halo 2: Anniversary, the confetti does not appear in classic mode.