Although only Max is available to use at first, Monica later makes her appearance upon entering the Miner's Breakroom. This final dungeon has a massive 38 floors! There are four dead ends containing mini-bosses, two break rooms, and the depths containing the final boss. Only two seals are present in the entirety of the dungeon - both of them being white seals. The gate key is the Trolley Oil, which is used to power a mining cart to advance to the next floor. Getting through blocked pathways requires the Rusted Key, which simply opens the locked door.
There is very little in the way of story this chapter because this dungeon is entirely optional, as you have technically already beaten the game to get here. However, even with ultimate weapons and some skill, this dungeon will still be a challenge for most players. It gets even harder as you go on by throwing stronger versions of the previous enemies, improving vastly in health. The Ridepod has surprisingly little defense against the stronger enemies, and so it is imperative that you build up your ultimate weapons to its maximum possible stats.
The time trial medals here are very easy to obtain, as every floor is given lots of time to defeat every monster, collect abs and gilda, and open every chest. As long as you aren't needlessly wandering around the map, you should be fine.
Like with earlier item-only stages, Poison Apples can be used to weaken most of the enemies, Holy Water can be used against undead enemies, and Final Bombs are recommended for taking down larger foes. Elemental Stones are great in Zelmite Mine, as many enemies have elemental weaknesses. The cannon-type enemies will cause a headache due to their tendency to shoot cannonballs and ruin your chances of a medal, use a Stone Berry or Heart-Throb Cherry to stop them, and finish them off with Elemental Stones or Final Bombs.
Spheda in Zelmite Mine can be difficult at first, but later becomes easy to get the hang of. Although the wooden support beams can get in the way, they can be used to make bouncing shots. Also note that the walls are jagged, and bouncing shots off them can be inconsistent. But other than that, there are very few off-course areas. The Flamingo works wonderfully in here, as curved shots can be very helpful and surprisingly easy to pull off.
For the boss battle with Burst One and Two, see Nail Burst.
The first dead end is accessed by taking the moon path from Crossroads of Destiny. It contains two identical mini-bosses, the Nail Bursts, and is optional in terms of completing the game. Winning this boss fight nets you a Healing Coin and a Sun Stone, which can be used to create the Nova Cannon IV if you've already used your other Sun Stone.
For the boss battle with the Exploding Skeletal Dudes, see Rare Jacket.
The second dead end is accessed by taking the moon path from Which One?. It contains eight Rare Jackets that will fight you all at once, and is optional in terms of completing the game. Winning this boss fight nets you an Absorption Coin and Moon Stone.
For the boss battle with the Flappin' Brothers, see Sphinx.
The third dead end is accessed by taking the moon path from Crossroads. It contains two identical mini-bosses, the Sphinxes. Unlike the other dead end bosses, this boss must be defeated in order to complete the game. Winning this boss fight will net you an Experience Coin, a Poison Coin, and Dynamite, which will be required in order to proceed past the cave wall in the last floor of the dungeon, the Zelmite Mine Depths.
For the boss battle with the Mandrakerz, see Mandora.
The fourth dead end is accessed by taking the moon path from Little Dragon Army. It contains eight Mandoras that will fight you all at once, and is optional in terms of completing the game. Winning this boss fight nets you two Diamonds.
This break room will reintroduce an old nemesis, Flotsam. He has returned with a new mechanized body thanks to his new boss, and will be eager to fight you. Take a snapshot of him to earn an additional scoop before defeating him.
For the boss battle with Mr. Big Shot Shadow, see Fake Genie.
Before proceeding, make sure you obtained the Dynamite from Dead End 3, as you won't be able to blast open the walls of the Zelmite Mine Depths without it. The depths contain a huge deposit of zelmite, but guarding it is the Fake Genie from the first Dark Cloud game. Be sure to take a snapshot of the zelmite and of the genie for additional scoops. Defeating the final boss will play the second ending to the game.