Alexander the Great Achievement
Alexander the Great50
Kill 2500 other players
This achievement will require you to be playing on a multiplayer server, whether it be your own private server or a public server. The best, and realistically the only way to get this achievement is to have someone help you boost. Ideally, that person could also be going for the "Meet Your Maker" achievement.
The simplest way to unlock this achievement would be to craft a few crossbows, several thousand bolts, and just kill your partner every time they respawn on their bed. One or two headshots should kill a person but you have to wait until the other person is fully respawned otherwise they will take no damage from the bolt.