I think I have a good idea for a skull.
It would either be called "Locust" or "Swarm", and it would work like this: Huge Swarms of Drones will pop up more occasionally then before. Unlike how Drones would be scripted to pop up, this skull would enable random Swarms of Drones to attack the player at any appropriate time in the game.
Now I'm working on how the Drones would work in combat. I think that some of the Drones would attack the Player with weaponry like usual, but some of them are released as "Unique" Drones. In previous Halo games there was just 1 type of Drone in the entire Swarm. I think there were different colors, but they were all pretty much the same, just with different weapons. Now I propose that different "Ranks" of Drone be included in the Swarm. Just like the Brute Pack in Halo 3, with Minors, Majors, and Chieftans. Though the Ranks in the Swarm would be different combat wise.
Here it is:
1. Drone Minor - Normal Drone, and main force of the Swarm.
2. Drone Jockey - Slightly lower-armored Drone that latches onto the backs of Elites (and possibly Brutes and smaller species) and fires at the Player with the safety of the Elites armor and body in front of it.
3. Drone Jockey Major. - Has the same amount of body armor, but Latches onto the backs of Hunters, and Enemy vehicles whenever possible. Maybe in groups of 2 or 3. Acts the same as Jockey Minors. The Majors would be colored differently or emit a different noise.
4. Drone Dragoon - lower-armored Drone, maybe being lower armored then Minors and Jockeys, that sits on Precarious far away locations, and attacks the Player with Carbines. Looks like a Minor with less body armor, and different coloring.
5. Drone Heavy - Drone with High-level-armor compared to Minors. Medium chance of Spawning. Is slightly bigger then regular Drones. Has long chain chords attached to it. Will attack the player with Concussion Rifles, and Storm Rifles. Will have normal flight patterns like regular Drones.
6. Thunder Drone - If the Drone Minor was a regular House Fly, then the Thunder Drone is the "Horse Fly" of the Drones. Extremely fast and agile. Will fly all over the place. The Thunder Drone is HUGE compared to regular Drones. At least half the size of Hunters. Coloration is random. It's eyes are Blood Red, and it emits a loud droning noise when it flies.
Will attack the Player with it's claws in Melee attacks. It will also pick up the Player and fly around before dropping throwing them back to the ground. The Player can try to melee the Thunder Drone while flying to make it drop them. Has a low chance of engaging the Player in a Quick-time event where it tries to kill the Player with it's blade teeth. Press a bunch of buttons or something and lower it's health or it will quickly leech you're shield and kill you.
There's a 25% chance the Thunder Drone will spawn with weapons, either duel Storm Rifles or duel Plasma Pistols.
7. Finally the "Drunkert" Drone. - Has a veeery low chance of spawning but acts like regular Minors. Spawns with random hilarious attire, like Clown costumes, and Party Hats. When killed the Drone explodes.