Bonehead Island is one of 11 accessible islands in the Great Sea in Paper Mario: The Origami King. It is found around the southeastern corner of the sea, just outside the reach of fog, and is one of the few islands not restricted by fog. It can only be explored after retrieving Captain T. Ode and his submarine from Musée Champignon in Toad Town. When Mario enters the Great Sea with Captain T. Ode, Bonehead Island is already charted in territory G-5 on the Sea Chart with a skull icon, allowing Mario to reach the island without getting lost in the fog. Aside from several Not-Bottomless Holes to be filled, there is only one Toad, one Collectible Treasure, and one ? Block on the island. A coffee shop is also found on the island, as well as a Snifit vendor from Fun, Funky, and Functional. This island shares similarities with Fortune Island from Paper Mario: Color Splash, such as a giant skull-shaped rock and a puzzle involving lighting torches.
When Mario, Olivia, and Captain T. Ode arrive on the island, Olivia describes it as spooky, noting that the large, hollow skull in the middle of the island appears to be staring at them. The captain tells them to explore the island, claiming there are secrets within. Mario must get off the boat onto the dock and head toward the skull. There are two Not-Bottomless Holes in the base of the skull, as well as one in the wall to the left and one in the ground to the right. Heading left, there is a Snifit vendor who sells the Gold Time Plus and Coin Step Counter accessories, a Fire Flower on the campfire, and two barrels containing confetti. Off to the right and down on a ledge, there is a ? Block containing a Shiny Ice Flower and a Not-Bottomless Hole in the wall. Patching it reveals a door to a coffee shop, where Mario can purchase a "Morbid Mocha" to initiate a conversation between a Dry Bones and a Bone Goomba.
To get into the skull, Mario must enter a hole on either the right or left side of it. If he uses the left hole, he can drop down onto a ledge to find a crumpled Toad that he can hammer to restore. As thanks for rescuing him, the Toad marks a spot on the Sea Chart where a treasure is to be found before joining the Snifit. Inside the skull, there are three rooms. The two rooms on either end have a nearly identical setup, while the middle room simply has a small skull in the middle with a flame in its left eye. This indicates Mario must hit the pillars in the other rooms to make them symmetrical. Doing this makes a button appear in the middle room, which Mario must hit to raise the skull and reveal a set of stairs.
Upstairs, there are a few barrels and crates containing confetti, as well as a treasure chest containing the only Collectible Treasure on the island: Submarine "Marino" (No. 74). Mario can then head south to exit this area and reach the outside, at the top of the skull. If he slides directly down, he will reach a small niche with a backwards Toad statue. Hammering the statue turns it forward to reveal a message: "If you seek paradise, gather the three orbs on Diamond Island". As Olivia ponders what this means, a massive, realistic fan appears in the background, blowing away the fog, allowing them to easily access the surrounding islands. The statue then reads, "Seek and ye shall find... Come, follow me to paradise...", prompting them to head out to follow the purple streamer.
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