One day playing a game of Halo 2 with my little brother, we found a really odd glitch.
1. Configure the gametype, so that there are random tanks(needed to get 2 different ones in the same level.) Also if you'd like to live longer, I recommend turning on the overshields :P
2. Start the game, use the map Coagulation.
3. Keep destroying the tanks...till you have both a Scorpion and a Wraith.
4. One player goes in the Scorpion, the other in the Wraith.
5. Now for the odd part, the player with the Scorpion just drives towards the Wraith and the player in the Wraith crashes into the Scorpion using the speed boost...
6. If done correctly, the Scorpion will fly off going berserk all over the map.
7. Feel sorry for the player in the Scorpion, as he is about to die a gruesome death :D
8. Even after the player in Scorpion dies and the tank blows up, it still has the tank threads flying around, killing everything in its path. (lol)
9. And if you wonder how to use it against the enemy? Well in the Metropolis level, you can use it and it COULD kill loads of enemies =x