The existence of many hidden skulls has been discovered.[1] These small objects are hidden in every campaign level in Halo 2, some levels containing more than one. Their effects, while somewhat disputed, can do anything from making the player invisible to removing his HUD. One, called "I Would Have Been Your Daddy," is a maddening skull that, unlike the others, seems to have no reliable mechanism for triggering its appearance. After finding it and picking it up, players are teleported to "Sniper Alley", the alleyway where a large number of snipers are normally, and are entered into a battle with 7 waves of Elites, each wave with the number of Elites equal to the wave number (wave one has one, wave five has five) using only a plasma pistol, with victory leading to new NPC comments.[2] However, the effect does not activate unless all waves are defeated.
The current known skulls are: Unnamed (text does not appear when collecting this skull, but has a name; see below), Thunder storm, Blind, I Would Have Been Your Daddy, Catch, Grunt Birthday Party, Famine, Envy, Assassins, Mythic, Sputnik, Angry, Ghost, Iron, and Black Eye. These skulls are only available on the Legendary mode except for the Blind skull, found on any difficulty in the level Outskirts. One skull shows no text when collected but examination of Halo 2 files shows this skull to be known internally as Whuppopotamous (fitting the acronym) and also Cowbell.
The Scarab's destructive main cannon is available as a handheld weapon. It is located in a hard-to-reach area in a level where the Scarab is present. To obtain the Scarab's powerful weapon you must first arrive at the end of a long bridge in the level Metropolis. After defeating all the enemies except one Banshee, the player must lure the Banshee into a tunnel and board it as it reaches the other side. After commandeering the Banshee, the player must fly to a certain grouping of buildings: the Scarab gun resides in the middle of a bridge connecting them. Although the Scarab gun uses the Plasma Rifle model, it shoots a huge green plasma beam many times larger than the Master Chief. This trick is most easily performed in Co-op mode, where you have another player to provide backup and assistance.