Brigadier Mollusque-Lanceur III, Dauphin of Bubblaine (simply called Mollusque-Lanceur) is the Boss of the Seaside Kingdom. His design is a cross between an octopus and a french noble from the Ancien Régime era. He holds a purple Multi Moon that will be dropped once he is defeated
He initially appears atop the large glass in the center of the Seaside Kingdom, sucking the water from it with a straw. In order to stop him, Mario must hit several Ground Pound Switches scattered throughout the kingdom, which will cause giant corks to be shot onto his head. After the first cork, Mollusque-Lanceur will attempt to stop him by launching Floating Mines that explode after a short period into the water around him. Once Mollusque-Lanceur has taken enough damage, he will leave the tower to confront Mario directly, now with a large puddle of lava on his head.
In battle, Mollusque-Lanceur floats around and will sometimes spite a Floating Mine or a drill-like cone shell. To defeat him, Mario must capture a Gushen and use its water to clear the lava off of his head, exposing it. He must then keep pounding his head with the water or Ground Pound him, until eventually, he is defeated. However, he can spin to escape Mario's attacks for a brief moment.
Mollusque-Lanceur can rematched in a painting found in the Mushroom Kingdom; the rematch takes place in a whole new area that features the large glass from the Seaside Kingdom, a platform with a Gushen that can be captured by Mario and rain to make sure that the Gushen never run out of water since the rest of the area is nothing but bottomless pits. While floating, Mollusque-Lanceur can now change his height, making him impossible to hit from above, forcing Mario to use the water propulsing the Gushen to hit Mollusque-Lanceur.
- Brigadier Mollusque-Lanceur III, Dauphin of Bubblaine's name is inspired by various French terms and words.
- Brigadier is a French military rank that can be compared to a Corporal.
- Mollusque-Lanceur literally means "Mollusk Thrower".
- Dauphin is a double pun since it can mean the heir of the French throne or a literal dolphin which of course play on the oceanic theme of the kingdom.