Fight Tartarus with a Banshee

In the last part of Halo 2 on the level The Great Journey during the Boss Fight with the Brute Tartarus, it is possible to Fight Tartarus with a Banshee. This may take a few tries to get on approach but it is well worth it as he is easier to take him down.

Instructions
In the second to last part of the level where Sergeant Avery Johnson destroys the door with a Scarab, wait for him to shoot the door then fly into it. It is advisable that you destroy the two wings of the Banshee before you enter the door. Although, with the two wings, you can still make it, but you'll just damage the wings and it will take a long time. After you get inside the door, start flying upward and then forward. You will fly over one wall and then get stuck in between two walls. When this happens, fly downward. Your Banshee will end up in front of the door.

At this point, get out of your Banshee, so the door will open, and then get back into your Banshee and fly into the room. When that is done, it will be a lot easier to move around. A few Brutes will engage you, but you can take care of them no problem with a Fuel Rod Gun shot; however, on Legendary, this may be a problem. The only other way on Legendary, is to simply fly in the door with your Banshee. After they are dead, get out of the Banshee so the next door will open and fly in. When you do this, a cutscene will show Tartarus activating Delta Halo. After the scene finishes kill the Brutes and then run backwards past Johnson. Your Banshee will be sitting in the hallway of which you can go into and fly through the pillars to fight Tartarus with.

Tartarus will call you a coward for doing this but a few Fuel Rod Gun shots should shut him up. This can be an extremely good method to use on Heroic and Legendary difficulty settings, especially as you have to face more than Tartarus at the very end.

Note: it is also possible to fight him with a Spectre using a similar method that involves climbing the outside edge of the structure with a hi-jacked Spectre.