These  cheats  are  ONLY  for  the Custom Edition of Halo: Combat
Evolved.  Open  the  properties  window of the Halo shortcut and add "
-console  -devmode"  to the end of the target field. Apply changes and
start  the  game  using  that  shortcut. Press [~] during game play to
display  the  console window, then enter one of the following codes to
activate the corresponding cheat function (codes do not work in online
games):

cheat_medusa <0 or 1>             Instant deaths for enemies 
                                  that see player
speed <0-20>                      Set game speed game
cls                               Clear console window
cheat_bottomless_clip <0 or 1>    Unlimited ammo and no overheating 
                                  for weapons
cheat_infinite_ammo <0 or 1>      Unlimited ammunition
cheat_super_jump <0 or 1>         Super jumps
cheat_bump_possession <0 or 1>    Possess touched character
cheat_deathless_player <0 or 1>   Invincibility
cheat_spawn_warthog               Spawn Warthog
cheat_all_powerups                Spawn all power-ups
cheat_all_vehicles                Spawn all vehicles
cheat_all_weapons                 Spawn all weapons
cheat_teleport_to_camera          Teleport player to current camera 
                                  position
quit                              Quit game