Halo: Reach

Download this gametype, and play with a second controller or a friend in a custom game:
http://www.bungie.net/Stats/Reach/FileDetails.aspx?fid=15149...

If you are having trouble with the above link, download the gametype from the following webspage:
http://halo.xbox.com/en-us/haloreach/PancakesLP/fileshare#%2...

Just have the person getting the achievement pick up the skull, and melee the other player(s), making sure to get the "oddball melee" medal. After 3 kills with it, the achievement will unlock in-game.

Note: It will only work if you play this gametype, and NOT regular oddball that the game comes with. You must use the gametype in the link!

Update: As of August 19, 2017, this method still works

When this DLC released, Bungie created special achievement game types on their website to make this easy to boost. Some people have trouble downloading these from Bungie.net, so I put them on my File Share along with a custom map to make things go quicker.

From the menu, select File Browser, New Custom Search, File Share Search, then enter my gamertag (Demonex Machina). Download "Oddball" and the map "Defiant DLC Achievements" (For all three Defiant Map Pack achievements, download everything).

With a second controller or a boosting partner, go to Custom Game, set the game type and map (The map is a Countdown variant) to the ones you downloaded and start the game.

Grab the skull and melee your dummy or boosting partner to kill them. Repeat two more times for your achievement.

You CAN win all of the defiant dlc achievements in CUSTOM GAMES!
Simply download this gametype to your xbox from bnet and load it up on reach:
http://halo.xbox.com/en-us/haloreach/PancakesLP/fileshare#%2...
[This gametype will work whereas the in-built oddball gametype will not]
So grab an extra controller or a mate and have at it =D (Thanks Joda X & Maka91!)
All credit for this youtube video demo goes to OpTicNiko.
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[!] You must get three kills in a single game with the oddball taking as long as you like,
the three kills do NOT have to be all in one life [but can be].
[!] You do NOT need to get a triple kill with the oddball [but you can].
[!] This does NOT have to be done on a defiant map [but can be].

This is how you do it legit for if/when they patch the custom games...
|> Load up rumble pit [preferably] or multi team or team objective and vote for an Oddball game variant
{All three of the defiant dlc achievements can be won in the team objective playlist}

- Once in a matchmaking Oddball game, run over to the oddball [marked on the HUD in white, or red if an enemy is in possession of it - if it's the latter kill the ball carrier]
- Retrieve the oddball by standing over it and holding the (X) button [by default]
- Now find a nook to hide in [people will be desperately trying to kill you at this point, try to evade them or kill them with the oddball melee instakill]. An example of such a place is the top of the lift on reflection.
- Wait for enemies to come near enough to you then melee them with the ball by pressing RB [the right bumper (by default)]
- When you get a kill an oddball kill medal will show up; amass three of these and pop goes the cheevo

NOTE:
~ The oddball kill medal appears as a red skull on an eight-pointed silver star [not to be confused with the killed oddball carrier medal which is a bronze skull with a red dot on it inside a gold octagon with a white background].
~ The oddball will dish out an instakill on all enemies [unlike a normal empty-handed melee].
~ When you take the ball you will be marked as a target on all enemies' HUDs so move from cover to cover, try not to remain exposed.

Oldschool Halo 3 players will remember an achievement much like this named 'Alas, Poor Yorick':
If you got this cheevo in the past you will remember that the most difficult thing was finding a game of oddball on the right map, whilst getting the 3 kills was more or less a walk in the park.

Hope this helps
Happy gaming

coreymawf

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All credit for this youtube video demo goes to OnyxMovies117.

For people who want to do this in a "legit" way:
*Go to Team Objective
When game types come up, you can vote for two different types of game modes to get this achievement: Oddball and Hot Potato.

Now, when you’re in the game, the hardest part of this achievement is getting the oddball from your other team mates. Put on sprint and make a run for it!

When you get the oddball, there are a couple of things you need to keep in mind. First, the game counts any melee kills (not just ones with the oddball itself) while having the oddball in your possession as an oddball kill. Second, NEVER, EVER charge people to melee them. Wait for them to come to you! Find a good place to camp and don't be afraid to let your team mates help you out as they weaken your opponents and cover you. The Oddball is an automatic one hit kill but it doesn't get you overshields!

Using this technique, you should get 3 oddball kills in no time! Remember, this achievement doesn't have to be in one life either.

*Alternatively, you can go to Rumble Pit and try to find a game of Oddball there. You can use the same kind of technique as you would in team objective. However, it is sometimes hard to find a game of Oddball in Rumble Pit and it may be difficult to get to the ball while fighting 11 other people. Then again, the games also tend to be much longer while playing in Rumble Pit too. (Note: This method remains unconfirmed.)

For this achievement you don't actually need to have the DLC.

Very simple, just score 3 melee kills with an oddball during a matchmaking or custom game, it doesn't matter if it's from behind, or an assassination, it also doesn't have to be done on a defiant map or in one life.

Also, using the game mode: Hot potato (where you carry a bomb around til it explodes and resets) also counts as a skull kill.
I got this oon hot potato, if i remember correctly

I'm not sure if everyone knows this but you can get this one without the dlc and there's a few more you can get as well