Kaijuu Monogatari/Fat Badger's castle

Finding everyone: After trying to challenge Fat Badger at his castle, you will fall through a trapdoor to an enormous underground cavern. In the process, your entire party will be once again split up. Just as when you started the game, each character will arrive in a corner of the cavern which corresponds with their starting location in the world. I.e. the Hero will be in the lower right corner, Kupikupi will be in the lower left corner, and so on. The monsters in the cavern are even stronger than the ones found just outside of the castle, so it is imperative that you rejoin forces as quickly as possible. Even being in a group of two will improve your chances to survive over being alone. The inns that each character starts in are along the far right and left sides of the cavern, so each player should begin by heading up or down to the middle of the cavern. The Hero and Kupikupi should make their way up, while Poyon and Babubabu make their way down, until the Hero and Babubabu meet in the middle, likewise for Kupikupi and Poyon. Then your goal should be to bring the Hero and Babubabu to the left, while Kupikupi and Poyon head to the right, until they all meet in the middle.

Cavern features: Just like the overworld above, the cavern is full of interesting locations and features. You begin in each of the four hotels, so remember their locations well. They are certainly no longer free, charging 120 Pearls per person, but you should have enough money saved up, and you will continue to earn plenty more in the cavern. There is a Revive House near the center of the top portion of the cavern, closest to the hotel in the upper right corner. Any characters who die alone will return to this location. There is another Revive House just to the south of the upper left hotel as well. There are a number of doors for which you do not yet have keys, and there are bodies of water which you must sail across. There are many walls which are so old that they may fall apart by merely searching them. Or you may find tiny holes in them, in which case you can use Dynamite to blow them apart. In a few cases, you may get attacked by an Elemental when you search. The cavern also has a couple of merchants. There are two near the middle of the lower half of the cavern that sell the remaining equipment which you party is still in need of, namely the Air Cane for Kupikupi, the Glacial Spear for Poyon, and the Earth Stick for Babubabu. However, the reach one of the merchants, you must use a boat to reach his room, and then you must approach him from the top in order to avoid falling through several trapdoors arranged in his room.

Collecting items: At this point, you must continue to assemble a group of items. It is possible to locate many of them through exploration and speaking with the many denizens of the cavern. But they are scattered throughout the cavern, and many of them are well hidden. Here is a list of the items you will need to collect, and in the rough order you should collect them.
 * Platinum Key:The platinum key is found to the right of the center of the cavern. There is a room that is completely filled with water which you must sail north to get through (there are two people stuck in cells behind a river to its right.)  Sail across the water, and enter the room above.  You are likely to get attacked by a Hyper Mole here, and in the room to the right, you are likely to get attacked by a Hyper Kong.  These are very strong bosses so keep your party's health up.  In the room to the right, you'll find a treasure chest containing the Platinum Key.
 * Silver Mirror:To find the silver mirror, explore the right wall of the cavern. Directly between the two hotels, there is a break in the river which confines two people in cells.  The river then continues to the right through the wall.  You must get in your boat and sail to the right through the wall, and continue on until you can access a room in the middle of the water.  Climb the steps and speak with the person in the room above.  He will summon a Bone King to challenge you.  Defeat him, and you will obtain the Silver Mirror.
 * Power Hammer:Above the configuration of square cells in the center of the cavern, you will see a small chest nestled above the left cell, which contains a Soldier's Friend. There is a small enclosed room below with yellow floor.  Search the right block above this room, and you will be attacked by an Elemental.  Defeat it, and the wall will disappear.  Then step into the room, and Search the leftmost block of the room to discover tiny holes.  Use Dynamite to blow up the wall (there are chests which contain Dynamite, or you may buy some for 1000 Pearls from a merchant.)  Then follow the flow of rooms as they head up and to the right.  You are likely to be attacked by a Cursed Bat, a Hyper Blue, and a Hyper Kong so be prepared to fight.  In the final room, you will find the Power Hammer.
 * Drop of Life:You'll need to the platinum key to get this. Just north of the room where you found the Power Hammer, is an opening to a room.  In the room is a locked door.  Use the platinum key to open this door and step inside.  Talk to the man, and he will explain the you will need the Aura Ball to reach Fat Badger, but that the ball's power will diminish unless you offer a drop of life.  Then he will give you the Drop of Life.
 * Golden Mirror:To the left of where you obtain the Drop of Life is a long room with an old man who walks about. You'll want to explore the entrance near the top, but walk around the outside of the room to avoid falling in the trapdoor near the middle.  In the room above, open the door with the Gold Key, then hop in your boat and sail over to the next door, which can also be opened with the Gold Key.  Then walk across the hallway to the left until you see a set of steps in the lower left corner.  Enter the room to the right of the stairs, and continue on to the next room to find a chest which contains the Gold Mirror.  Watch out for attacks by a pair of Death Centaurs when entering and leaving the room.
 * Bakery:After collecting the Golden Mirror, exit from the rooms and investigate the staircase in the corner. You will arrive in a room that appears to be a bakery.  Speak to the baker above and he will give you a French Bread.
 * Devil Key:To the left of the room where you started your search for the Golden Mirror, there is a river that passes through the north wall of the cavern. Sail through it, and open the door that you find with the Platinum Key.  Enter into the following room, and you will find two goblins.  One of the goblins made the Satan Key and that it's in the next room, and he will attack you.  Defeat him, and then walk into the upper right corner of the room and Search the right wall.  In the next room, you are likely to be attacked by a Dragon Snake.  Just before you investigate the chest in the upper right corner, you will be attacked by a Gold Kong.  Open the chest to find the Devil Key.
 * Flame Sword:The Flame Sword is the best weapon that the Hero can equip. It just so happens that two such swords can be found in the cavern, and finding both has an interesting effect.  The first Flame Sword is very close to the upper right hotel.  Walk down and to the left, and up the hallway to the dead-end.  Search the middle of the wall to the right, and then open the door with the Gold Key to find a man who gives you a Flame Sword.  The second sword is close to the upper left hotel.  Come down, and then head to the right.  When you see a body of water in the shape of a plus sign (+), walk up the hallway above, and explore the wall on the left.  Searching one of the walls will summon an Elemental.  Defeat it and proceed inside.  Open the door above with the Gold Key, and search the lower left wall in the next room.  Keep going inside, and be prepared to face strong monsters like a Gold Mole.  Talk to the man in the room to obtain a second Flame Sword.  He will warn you that in order to use both swords, you will lose some of your protection.  If you say yes, your offense will increase by 30, but your defense will decrease by 30.  There is a man, Fencer Saga, found in the lower right corner of the cavern behind a search-able wall who teaches you about using one Flame Sword in each hand.