Pirate Plunder is a multiplayer game mode. While the achievement description states "map" it is really referring to "game" as there is only one map available with random treasure chest and mine spawns. You can easily boost this by having an opponent quit after you capture one treasure chest, which takes about 30 seconds.
Note that this achievement can only be unlocked in a ranked match.
When you start the game, move toward your minion spawn point directly in front of you, hold down to select it and press ten times so that you have ten minions. Go down to your ship at the water's edge and use to sweep your minions into the hole in the middle of the deck. One will fly forward to act as lookout, and one will fly backward to the stern of the boat to drum a cadence for the rowers. You should have the number 10 in a red circle above the hole. If you don't, it means some of the minions missed, so use to guide them in. When your ship is fully manned, move to the stern where a white circle will have appeared. Press and you can then move your ship about the lagoon. serves as your accelerator, and you can steer with the .
There are chests and mines floating in the water. You can safely hit three mines without sinking, but you only need one chest to get the minimum score of 75. At this point, your partner can quit out and you will earn a win, unlocking the achievement.