North of the map stone (and northwest from the Quest for the orc), look for a Morgul-locked chest.
Take the path south along the small platforms sticking out of the water and smash the 7 plants there within 5 seconds of one another and the brick will materialize. Dig up the Lego dirt here to uncover a plant that spits out a brick. Shoot it and jump on the lily pad to the three narrow beams and the island beyond. Right next to Mithril brick #3, look for a target sticking up from the water. Walk south, over the beam connecting the islands, and look for a dark nook where you can use Frodo to uncover another brick. Head to the western-most point of the Dead Marshes and jump up the pillars jutting up out of the water to reach the brick. Head south of the path into the Dead Marshes and jump over three springy leaf plants, then jump up onto the elevated ledge and defeat three ghosts to obtain a Mithril brick.
