Halo

Alternate ending sequence:
Successfully complete the last level of the game in campaign mode under the legendary difficulty setting. The new ending features a human and alien fighting hand to hand. The human will say "Its over", and then they hug because they know the explosion will kill them both. Also, the FMV sequence of each battle scene will be slightly longer.

Alternate dialogue:
Playing under the legendary difficulty setting introduces new dialogue not heard in other modes. For example, after being massacred by a force of Grunts, Jackals and Elites, one of the grunts asks, "Can I have his helmet?". Also, your fellow Marines seem to be a bit more chatty (as well as profane).

Under the legendary difficulty setting, view the entire first FMV sequence. During the sequence, the General says things very differently when compared to the sequence under the easy difficulty setting.

Glitch: Demo version: Silent Cartographer: Enter secure room:
When you are in the Silent Cartographer room the first time, get in the Warthog and drive in fast. You can make it through the door without having to get to the security override. If you do not make it, equip a pistol or assault rifle. Walk up to the locked door. If you are centered enough, you should see the energy sword person's head through a small pane of glass. Shoot him repeatedly in the head and he will die.
Information in this section was contributed by John Cimino.