Bowser Nightmare is an unlockable board that appears in Mario Party 5. This board map continues the Bowser-themed boards that have appeared in the previous installments. Bowser Nightmare is the largest board map in Mario Party 5, and is unlocked after the player completes Story Mode.
Bowser Nightmare does not follow the dream theme of the other board maps that appear in Mario Party 5. Instead, the board map is created from Bowser's wicked and demented dreams. Bowser Nightmare is a large board that is surrounded by lava. The board itself resembles a castle and has carpeting near the bottom of the board, while the top contains tiled floors. The brim of the board is filled with torches that contain Podoboos. The board is filled with happening spaces that are hosted by Bowser. The happening spaces in front of the buildings that are found in the bottom of the left and right hand side of the board will trigger a Bowser strolling event. During this event, Bowser will take a stroll around the board, causing any character that he crushes to lose coins. There are numerous statues of Mario series characters found at the top right and left hand side of the board. If a player lands on one of the happening spaces in front of the statues, Bowser will appear in his Koopa Klown car and force the player to choose between two colored blocks. At the top of the board, there is a giant flamethrower with a few happening spaces on it. If a character lands on one of the happening spaces, Bowser will activate the flamethrower, causing any character that gets burned to loose all their capsules. Finally, there are two happening spaces in the center of the board that surround the circle. If a character lands on one of the happening spaces, they will be transported into the center of the circle.
- Capsule Machine - The Capsule Machines is a vending-machine like character that dispenses capsules to characters that approach it. Once they land on the arrow pointing towards the Capsule Machine, it will ask them if they want a capsule. If the character accepts it's offer, then the Capsule Machine will dispense a capsule for no charge. However, the Capsule Machine will not dispense a capsule if the character has too many capsules, or if it is the last turn.
- Bowser's Stroll - On each side of the board map, there will be a structure with a happening space in front of it. When a character lands on the happening spaces, Bowser will exit the structure and take a stroll around the board. Along the way, he will turn any Blue Space he comes across into Red Spaces. At the same time, he will take ten coins from any character that is in his path. The red spaces will return to normal after a few turns have passed.
- Bowser's Koopa Kar - Near the top of the board, there will be several statues of Mario characters. If a player lands on the happening spaces situated in front of the statue, Bowser will force them to either hit a blue or red block. One of the blocks will send the character back to start, while the other block will cause them to lose coins.
- Bowser's Flamethrower - At the top of the board, there is a giant flamethrower with several happening spaces in front of it. If a player lands on one of the happening spaces, Bowser will activate the flamethrower, causing any character that is in its path to burn and lose all their capsules.
- Bowser's Circle - In the center of the board, there are two happening spaces located around the center of a circle. If a character lands on one of the happening spaces, they will be transported by a warp pipe to the center of the circle. The circle contains nothing but red spaces and happening spaces. In order to exit the circle, the player must land on one of the happening spaces.