"Fight off 8 unique players during your time on top during Land Grab in Multiplayer Free Roam."
Just in case the requirements of this achievement aren't clear, you have to:
- Start a Land Grab match in normal or hardcore free roam. Friendly free roam doesn't have Land Grab. It can be either a private or public session.
- Kill 8 unique attackers in that match while you're in possession of the land. If you lose your claim during the match, you can reclaim it and continue where you left off. If the match ends before you get 8 unique kills, you'll have to start over in a new match.
- "Unique" attackers means 8 different players. Killing the same player more than once won't count.
- Players in your posse don't count as attackers.
- To maintain your claim on the land, you have to stay inside the blue circle, but the attackers don't have to be inside the blue circle when you kill them. (Thanks to DeceptiveTen for the info.)
One way to unlock the achievement is for 9 or more players to boost it together in a private free roam session. You can probably get 2 or 3 or more players boosted during one Land Grab match. After the first match is over, the whole group will have to transport over to another town and start another match. It should only take about 30 minutes to get everyone boosted, assuming everyone has headsets and is working together. (Afterward, you may want to make sure everyone has the "Posse Up" achievement before everyone goes their separate ways.)
If you want to earn this achievement legit, I wish you luck, because I don't think it will be easy. The biggest problem with attempting this achievement in a random public free roam is that you can't count on 8 players challenging you. Even in a full free roam, a few players are probably going to be clearing hideouts, working on public enemy challenges, or whatever, and they won't drop what they're doing to play Land Grab with you. Unfortunately, you have no control over this, and it's why boosting might be necessary.
If you still want to try getting it legit, first make sure you have decent weapons: dynamite, high power or Mauser pistol, etc. Don't try this at rank 1 with nothing but a Cattleman revolver and a melee knife. If your rank is low, get weapons from hideouts or from killing higher-ranked players. Also, it wouldn't hurt to clear out one of the Liars and Cheats hideouts first, so you can bring the explosive rifle with you.
It will also help to use casual aim, to boost your ability to lock on to targets. This is no time to be an auto-aim snob! To do this, go to Options, Config and change your multiplayer targeting mode to casual. You can change it back to normal or expert after unlocking the achievement.
As you get kills, invite the players you've killed to join your posse. One reason for doing this is to help you keep track of who you've killed and who you haven't. The other reason is that if they join your posse, they may decide to stop trying to kill you, and you may even be able to convince them to help you.