Assassin

The Assassin Medal is awarded and achieved for meleeing an opponent from behind. It is available in all Multiplayer gametypes and has a Bungie difficulty rating of 2 out of 10. It is represented by a ninja face on a shruiken star after you kill an opponent by meleeing the player in the back, a message appears on your screen that states: "You assassinated (player's name)". The Assassin Medal is also a medal in the Halo 3 campaign when Campaign Scoring is turned on and activated in the Meta Game. It is a very common occurrence in multiplayer.

The victim can sometimes avoid this by turning around before the attacker has a chance to get a hit in, as it will count as a normal beatdown, though there are rare occurrences where this will still result in an assassination. There are also occurrences where direct frontal punches results in an assassination, while assassinations sometimes result in beatdowns due to the attacker meleeing to the side. An assassination can be gained by hitting the right shoulder whilst hitting the left will be a beatdown and not an insta-kill.

If you assassinate three players on a Legendary Map Pack map, either Avalanche, Ghost Town, or Blackout, the achievement "Came...From...Behind" is unlocked for 50 Gamerscore. Also, the achievement can be earned on a Mythic Map Pack map, Assembly, Orbital, or any Sandbox variant.

Trivia

 * There is also a popular fake variant of armor going around on Halo 3 known as the Assassin armor, which is really a photoshopped fake made by splicing together pictures of other armor permutations.
 * In Halo 3, even an invulnerable player can be assassinated.
 * It is possible for two players to assassinate each other. This happens mostly when one player jumps over the other, the other one below looks up and melees whilst the one flying over looks down and melees. If timed well, they will assassinate each other.
 * One way to assassinate someone is to jump right before they try to assassinate you. Once you jump, melee and you will assassinate them. This is sometimes be difficult to perform, but your radar can be a useful tool when attempting this.