Successfully complete the last level of the game incampaign mode under the Legendary difficulty setting. The newending features a human and alien fighting hand to hand. The humanwill say "Its over", and then they hug because theyknow the explosion will kill them both. Also, the FMV sequenceof each battle scene will be slightly longer.
When you are in the Silent Cartographer room the firsttime, get in the Warthog and drive in fast. You can make it throughthe door without having to get to the security override. If youdo not make it, equip a pistol or assault rifle. Walk up to thelocked door. If you are centered enough, you should see the energysword person's head through a small pane of glass. Shoot him repeatedlyin the head and he will die.
Obtain the indicated skull to get the corresponding effect.
Simply beat the game on legendary to unlock an additional scene at the end cinema.