Driving A Destroyed Vehicle
From Halopedia, the Halo wiki
This is a "trick" that allows you ride a destroyed vehicle. You can't drive it, only be in it while destroyed.
You need two people to do this. First, go to any level or a multiplayer map and have someone (Person A) stand next to a damaged vehicle. Next, someone else (Person B) has to stick the person next to a vehicle with a plasma grenade or Spike grenade. As soon as Person B sticks Person A, the latter has to get into the vehicle with Person B boarding it. The grenade will kill the driver but not the person boarding it. The vehicle will explode (if you damage it) and Person B will be occupying and riding the destroyed vehicle, but will have very limited movement because the vehicle is considered destroyed. It also can happen if the vehicle is lasered, and is a common occurrence on Snowbound in the Lone Wolves playlist. There is, however, a greater chance of the player blowing himself up and resulting in the loss of a life.
This can be done in campaign on the level The Ark. Using a Plasma Grenade and a Brute Shot, you must attempt to to destroy the Banshee that the Arbiter will get in. If done correctly the Arbiter will be on the floor laying in the destroyed Banshee. It is possible to do this in a multiplayer game. It has been reported to happen on Valhalla. When a player trys to board an enemy banshee, and a laser hits that banshee, sometimes the player proceeds to drive a destroyed banshee. This also can happen if a person with an overshield hijacks a Banshee as the player getting hijacked rams a wall and destroys the Banshee. Instead of dieing, the overshields protect the hijacker and leave him/her riding the destroyed Banshee.