Please read my full post: This achievement requires you to get 3 Oddball melee kills in a Legendary or Mythic match.
If you've been playing Halo 3 online since the game came out, then you probably already have this achievement. However, if you, like me, do not yet have Alas, Poor Yorick, you're pretty much screwed. Getting the Oddball melee kills isn't wildly difficult, but finding a Legendary or Mythic Oddball match nowadays is near impossible. IMHO, this is currently the hardest Halo 3 achievement.
Fortunately, I know the best way of doing this even though it's still a real pain. If I can get 8 of us together, I'll message everyone via Achievement Hunter to arrange a date and time to just play until we all have it. This can easily be done in 1 game, so once we get a match, we'll pretty much be home free.
Here's the trick: In Rumble Pit, Odball shows up 11% of the time. When everyone has all DLC, each Rumble Pit map is equally likely to occur. I estimate that if we see 35 games come up (including all the ones we veto) we should have 1 or 2 shots at this. If anyone can think of a better way, please let me know.
If you want to do this with me, comment your Gamertag and let me know if you have all the map packs. I'm sorry, but if you do not have all DLC, I won't be doing this with you.
My Gamertag is ReguLatency. Thanks guys and I'll see you online!