Getting to World 4 in Mario DS is a crucial step in the game’s progression, as it unlocks new levels and challenges. To access World 4, players must first complete the first three worlds and defeat the bosses in each one.
Once the third world is completed, players will be able to enter a warp pipe that leads to World 4. This warp pipe is located in the castle at the end of World 3. Players must then navigate through World 4, completing levels and defeating enemies, until they reach the final boss, Bowser Jr.