World 4 (Puzzle & Dragons: Super Mario Bros. Edition)
From the Super Mario Wiki
World 4 is the fourth world in Puzzle & Dragons: Super Mario Bros. Edition. This world takes place in a beach, resembling that of World 4 from New Super Mario Bros. Wii, with a remixed hula version of the world theme from that game. Like other worlds in the game, Orbs are scattered about the map. This world consists of twelve levels and a Toad House. Wendy O. Koopa is the boss of this world and is fought in her castle and airship. Clearing World 4- unlocks Boo Mario and Boo Luigi as Leaders.
A more difficult version of World 4 exists as a Special World: ★World 4.
Upon reaching the branching path in the Ghost House, the player may notice a Gold Block in the center, between the Warp Pipe and the sign. By hitting the block, the player can access a secret area, which leads to the secret exit of this course. In order to use the block, however, the player needs to clear more Dark Orbs than both Water Orbs and Fire Orbs. This course does not contain any Dark Orbs, however, so the player needs to bring an ally that can create them. Upon defeating the boss at the end of the secret path, the player unlocks World 4-4.