Before going to Moria, you seek a contract with Gnome.
Cave of Spirits
To reach the Cave of Spirits, take the ship from Alvanista to Beladum, then go south across the bridge, then go east and enter the cave.
In the cave, go north from the stairs, go east across the bridge, and go north until you reach a door. Try to go through it, and you will be asked for a password. In the SNES version, the password is ki, ku, ri, mu (3, 1, 2, 4). In the GBA version, it's ki, ku, ri, n. In the PlayStation version, choose numbers 4, 4, 1, 1. After the door opens, go down the stairs.
Help the Gnome
Go down the stairs, then go south through the door on the left. Talk to the gnome on the right and choose to help it. Walk slowly to allow the gnome to follow you. To make the gnome go to the next room with you, make sure that the gnome is standing next to you. Go down the stairs.
If you approach any of the gnomes in this room, they will attack you. If this happens, use Tractor Beam on the Clay Idols, because their defense is too high for anything else to affect them. Go to the south wall, then go to the west wall, then go north to the next room.
Now go north, then east, and you will find the gnome's friends. Your gnome will go with them. Go east and then south down the stairs.
Cross the bridge and go through the door. From the save point, go east and flip the switch on the wall. When the gnomes come running, go back to the save point and go north. Don't go through the door yet.
Set Mint's tactic to Value HP over TP. Set Arche and Klarth/Claus's tactics to not cast spells. Cless/Cress should be equipped with the Lightning Bolt skill. For short range skills, he should equip Tiger Teeth if he knows it, or Blade Storm if he doesn't. Make sure that Cless/Cress does not equip Psion Bolt, because that heals Gnome. Change your formation to put everyone in the center.
If you have not already done so, you can make four Flame Mantles to help in the next battle. If you have a Mantle or Aqua Mantle, just use a Rune Bottle on it to turn it into a Flame Mantle. Mantles can be purchased in Beladum, and you can buy Rune Bottles from Alvanista's item shop, but it's expensive. If you do this, make sure that you equip everyone with a Flame Mantle.
It can also be helpful to use Rune Bottles on Hourglasses, if you have any, to turn them into Chrono Glasses, but since Hourglasses can't be purchased, and since Chrono Glasses are very useful in a battle much later in the game, you might want to save your Hourglasses for later.
Go through the door to start the battle. Gnome will frequently disappear into the ground and launch itself in four missiles. You can't target it during a missile attack, so you have to just wait for it to stop. It will eventually become four shadows on the floor, and the shadows will all move toward a single point. When the four shadows converge, Gnome will come out of the ground and be vulnerable. However, Gnome has a tendency to launch into another missile attack almost immediately, making this battle very time-consuming.
You can use Hourglasses/Chrono Glasses to temporarily freeze the Gnome if you wish, but as mentioned before, Hourglasses cannot be bought, and they are very useful in a later battle, so you might not want to use them here.
However, the quickest way to defeat Gnome is to use a Chrono Glass, then have Cless/Cress use Lightning Bolt as many times as possible before the effect wears off.
Overall, Cless/Cress's Lightning Bolt does a lot of damage. Focus on having Cless/Cress stay far away from Gnome so he can keep using Lightning Bolt through the whole battle, whenever Gnome is targetable. You can try to have Mint cast Hammer right before Gnome comes out of the ground, for a chance to stun it. Cless/Cress's Tiger Teeth and Blade Storm skills also have a chance of stunning Gnome, but this should only be done as a last resort since Cless/Cress's Lightning Bolt does so much damage and can only be used from long range. Arche should use Thunder Blade, or Tractor Beam if she doesn't have Thunder Blade, and Klarth/Claus should use Ifrit (if he has it) or Sylph.
Gnome's Cave, Part 2
The ?Book that you receive is just a weak weapon, so don't waste a Rune Bottle on it. Open the chest to get Stone Wall, a spell for Arche. There are no more attack gnomes in the cave, so you do not have to worry about them on your way out.
Go west, then north up the bridge. Go northwest and go through the mountain pass, then make your way north to Venezzia. Go east from the fountain to reach the dock, and take the ship to Alvanista.
If you can afford it, buy six Rune Bottles from the Alvanista item shop.
Then exit Alvanista to go to the overworld. From there, go east, then south until you can go southeast, and go southeast to find a dock. Take the ship to Freland.
Go east from the dock and enter the village.
Walk up between the upper-left houses to find a chest that contains 2600 gold. Go to the south entrance of town and walk east to find another chest, which contains a Mixed Gummy/Melange Gel.
In the item shop, if you can afford it, buy two Silver Capes and use a Rune Bottle on each to turn them into Princess Capes. (Rune Bottles can be purchased from the Alvanista Item Shop.) Equip the Princess Capes on Mint and Arche. Use a Rune Bottle on a Mantle or Aqua Mantle to turn it into a Flame Mantle, and equip it on Cless/Cress. Equip Klarth/Claus with the Garnet Ring. This gives everyone protection against fire.
Buy Remedy Bottles at the Pharmacy.
Equip Cless/Cress with the Ice Scimitar that you won after the battle with Meia. It works well against the fire enemies in the next area.
Change Arche and Klarth/Claus's tactics to cast many spells. Turn off all of Arche's fire spells, have Klarth/Claus ready to summon Undine if he has it, and don't equip Cless/Cress's Phoenix skill if he has it.
Go east of the village to find the Molten Cavern, also known as Ifrit's Cave.