Tank Dropper

Tank Dropper is one of the the newest Halo 3 achievement that is gained by getting a kill while in Monitor mode in one of the Mythic Maps. Therefore, this is only possible to achieve in Forge. The most common way to get a kill in Monitor mode is to drop something on an opponent, such as a Fusion Core, or as in the medal's name, a tank. It is worth 25 Gamerpoints.

It is represented by a Monitor next to a dead person, with three stars in between them.

Methods
1. Start up Forge on Sandbox. Go into monitor mode and spawn any vehicle or object and get an opposing player to stand still below you, and then drop it to splatter them; however, the best option is to spawn a Scorpion Tank, as this covers a much larger surface area, is heavier, and so is the easiest object to get a splatter with.

2. Another way to do this is to stick a grenade to a person and quickly switch into monitor mode before it explodes.

3. Yet another way is to sign on a guest on a different team; launch a rocket across a Mythic Map at your guest; and then switch to edit mode, before the rocket lands a kill.

4. One more way is to smack an enemy with a large object with a baseball bat-like swing.

Note: The Killball does NOT count as your kill since it counts as "killed by the guardians."

Trivia

 * Currently, this is the only Mythic Map Pack multiplayer achievement that can be earned while offline.
 * This achievement is most likely the easiest achievement to unlock, due to the quickness and ease.