Skulltaker Halo 2: Anger
From Halopedia, the Halo wiki
Skulltaker Halo 2: Anger is an achievement in Halo: The Master Chief Collection. It is awarded for collecting the Anger skull in Halo 2: Anniversary on Gravemind while playing on Legendary difficulty. The achievement is worth 5 Gamerscore, and the Xbox achievement art is a still of Tartarus branding Thel 'Vadam with the Mark of Shame from the Halo 2: Anniversary opening cutscene from Cairo Station.
Location[edit]
After you save both groups of Marines, continue until you reach the first outdoor area with dirt and vegetation. Take a right as you enter this room and run up to the wall past the Gravity Lift that leads up to the sniper point. Get on top of the wall by going up the dirt mound on your left. Follow the wall and an invisible Gunner Grunt will spawn wielding a Fuel Rod Gun. Kill him and reach the floating Skull called "Anger".