Bowser's Gnarly Party
- “I built this board to celebrate Master Bowser's greatness! You'll love it, or I'll tell on you! Master Bowser is the best! If you don't see him now, you'll certainly see him later! Bwaha!”
- —Koopa Kid, Mario Party 4
Bowser's Gnarly Party is a board located above a sea of lava in the game Mario Party 4. It is hosted by Koopa Kid. He built it in honor of Bowser's greatness and wanted the players to have fun on it – whether they wanted to or not. Here, Koopa Kids were everywhere, and were put in charge of the games and shops.
The main attractions of this board are the two stone bridges, and of course, Bowser. Every time a stone bridge is crossed, pieces of it will crumble off. When it is crossed three times, it totally collapses and a new one appears leading in a different direction. Bowser is always on his platform somewhere on the board, waiting for a character to pass him (and changes his position every time a player gets the Star from Koopa Kid). He does different things to players depending on what size they are.
If a player gets to him at normal size, he will take away half of their coins (but gives fifty coins to players that have none). If a player gets to him while miniaturized, he will use his fire breath to send them to a different starting point in the middle of the board. If a player gets to him in their mega form, he will challenge them to one of two minigames. It can be either Bowser Wrestling or Panels of Doom. If the player loses, half of their coins are taken away. Victory results in Bowser leaving the board until the next Star is taken.
Also, every now and then, Bowser uses his magic to make everyone miniaturized for that turn. Landing on Happening Spaces is rare here, but is not advisable anyway, for landing on one makes the Bowser head statue in front fry the player in blue flames, destroying one of their items.
The Item Minigame of the board involves a Koopa Kid with three boxes (Also known as Koopa Kid shuffle or Mini Bowser shuffle). He puts an item in each of them then shuffles them around. After that, the player chooses one of them. However, they don't get the prize of the one they choose, that box instead becomes locked. After eliminating 2 boxes, Koopa Kid gives the item in the remaining box to the player. The Coin Minigame involves a Bullet Bill (Known as Brake Bullet Bill). Koopa Kid shoots one at the player, and they must find the power to hold it back with only their hands (as surprising as that sounds). Tapping 
repeatedly slows it down. They will get high amounts of coins if the speeding bullet doesn't go far, and not too many if it covers a good distance.
In Story Mode, if the player beats their opponents on this board, it will be unlocked to play in Party Mode. It is not necessary to defeat Bowser in his mini-game to get the presents back for this unlockable.
