In Lego Pirates of the Caribbean, there is a bonus mission you can unlock, and must unlock in order to get the 85th gold brick in the game for 100% completion.
To unlock the bonus mission, you need to find the first 84 gold bricks. There are four gold bricks per mission, for a total of 80 gold bricks received during missions. You get one for completing the mission, one for getting True Pirate, one for completing the Minikit in freeplay, and one for finding all eight compass items in the mission. The other four gold bricks are found at the Watchtower area in Port Hub when you complete all of the Minikits in a story.
Once you have your 84 gold bricks, go to the town area of Port Hub and assemble the gold pile near the cannons and you’ll build a gate to the bonus mission. Complete the bonus mission to get your final 85th gold brick.
