Mt. Gulg is another five-floor dungeon like the Terra Cavern, but unlike the Terra Cavern it is chock-full of nice Treasure. The big prize here is the Ice Brand, one of only two shared-chest items in the dungeon. As you might expect from a volcano, many of the Monsters here are fiery in nature and are weak to IceSpells. You don't have Ice3 yet, so you'll have to rely on Ice2 to exploit that weakness. Fortunately Marilith, the Fiend at the bottom of Mt. Gulg, has no elemental weaknesses at all, so there's no reason to save your attack Spells for her.
Mt. Gulg B2 consists of a short hallway with an large maze-like room filled with optional Treasure. Aside from the Claymore, most of the Treasures are money or gear you've seen before. The rest of the Treasures are found on the bottom two floors of the dungeon, which you will only reach after going up and down a number of times.
The new terrain gimmick in Mt. Gulg is the lava-covered flooring, which will deal 1 damage per step to each living party member. On the upside, you will not encounter any random enemies on these floors, so it can be advantageous to stick to them as much as possible. The encounters are, after all, likely to deal more than 4 damage to the party.
While MonsterSpecial Attacks have been relatively uncommon up until this point in the game, Mt. Gulg features a large number of foes with them. In particular, many Monsters have some variant on the Blaze Special Attack, which deals Fire damage to the whole party. Each Monster's Blaze deals a different amount of damage, so check the Monster pages to determine which are dangerous and may warrant casting a NulFireSpell.
B5 is a large floor with eight passages leading from the center. If you collected the Gold Needle above, the only directions that you need to worry about are west (where you will find the Flame Mail) and southwest (where you will encounter Marilith). At this point in the dungeon it is probably best to conserve your energy by avoiding unnecessary encounters.
Marilith is a strange boss. You may expect her to be vulnerable to Ice, but she actually resists every basic attack Element. She is the only enemy in the game vulnerable to Status magic, though, so a combination of Slow1 and Silence can render her attacks entirely impotent.
Gurgu Volcano is another five-floor dungeon like the Earth Cave, but unlike the Earth Cave it is chock-full of nice Treasure—and empty of Undead. The big prize here is the Ice Sword, one of only two shared-chest items in the dungeon. As you might expect from a volcano, many of the Monsters here are fiery in nature and are weak to ColdSpells. This dungeon also introduces the damaging floor mechanic in the form of lava.