The Swamp

I wanted to provide some answers, but they aren't there. I could try to force something out, but that wouldn't work. I'm going to push on, and let the answers come later when my mind is in the right frame to provide them.
Leaving the monk's cabin, the journey back to the main trail seems to take mere minutes compared to the climb up, and if anyone glances back the way they came, there is no sign of cabin, monk or trail. They all appear to have vanished without trace. In truth, the monk was able to warp reality slightly to invite the party into an extraplanar space designed to fit in with their real surroundings.
Traveling west, the prominence of the volcano grows until it dominates the horizon before you. The last remnants of shrub fall away. The valley stretches out before you to the north, but the land revealed is unlike anything you have encountered elsewhere. There are long arms of rock and slag stretching out like snaking roots from the volcano itself, creating undulating valleys and large flat ledges stepping down away from the peak.
Oozing and seeping down, through and across this landscape is a foul, slow-moving sludge of lava mixed with water, earth and slime. This creates a nasty terrain that is tricky to navigate, with many swamp-like features. There are dead-end passages, oozing pools, and streams of slime everywhere. Coupled with the thermal veins running beneath the entire mountainside, erupting sporadically in plumes of steam or lava, the way forward is unpredictable.
With sinking hearts, the party looks out over the quagmire. They have little faith that their map holds any promise of value. Imogene steps forward with confidence and urges you to shrug off your hesitation and follow her lead. She insists that even though the terrain is open, there are definitely places to hide concealing watchers. You need to get out of sight quickly. She is also certain that the map is accurate and will be of use.
She has been studying it as much as she can, and believes that once you can locate the initial marker on the map, she can follow it from there. The trick will be finding the initial marker...

Monk Matters

The githzerai monk is a mysterious fellow. He contents himself with relaxing on his porch, inviting you all to join him for tea. The libations are unimportant, he can conjure what he needs, his intent is to question you. His method of questioning is to remain silent as much as possible and let the silence open your mouths.
When he is asked a question, he will respond promptly, although he may pause to consider on occasion. His answers are as mysterious as he appears to be, and are guided by his understanding of the questions asked more than by their phrasing.
Asked about the dragon, he might say "the terror spreads over the land like his unfolding wings." Asked about the cult, he offers "there is treachery afoot, beware the illusion." Similar cryptic things pour out of him. It's hard to define this here when much of what might be said depends on what is asked.

Possible topics:
The Swamp:
The Dragon:
The Cultists:
The Shrine:
The Dream:
Ference Trensal:
The Necklace:
The Axe:
The Green Gem:
The Map:
Aron's Bowl:
The Dragon's Lair:
The Volcano:

I'm going to stall again to work on the responses...

Minor Reset

Backtracking a little in order to bring this together a little tighter before continuing on, the party left the giant stronghold after an encounter with the dragon. They started across the ridge line trail, approaching a forest. As they passed through the forest, the sound of rending noises came to them from their left. Moving through the trees, they discovered a pair of manticores devouring a bear corpse.
Following this encounter, they rested in the forest. While resting, the ranger Everett, who they encountered in their first foray along this quest, appears to one of the party members in a dream. Everett relates his story about the dragon cult and the necklace they seek.
After this, they continued on their way. While traveling through the far edges of the forest, they were overcome by a strange mist, and a compulsion to leave the trail for a suggestion of a path up into a narrow, well-concealed pass. At the end of the path, they found a small cabin with a githzerai monk resting on its front porch. He offered you dinner and lodging for the night, as well as whatever insight his travels have accumulated.
The monk's responses are given without hesitation, but are often cryptic and muddled. Too many times they appear to answer totally different questions than those asked. The monk is oddly serene. He seems keen to answer questions, and will respond when asked, but he prefers not to volunteer information.
Some time after leaving, but before the party reaches the edge of the swamp, they will have an encounter with Ference Trensal. After this, the trail will lead into the swamp and beyond.
When we return, I think it will be time to consider in more detail the responses of the githzerai monk.

Trensal Redux

As Ference aged and took on more jobs, he began to question himself about who he was, what he wanted and where he expected to go in his life. He was forever grateful to the dwarves who took him in and raised him, but as a human there were many ways in which he could never fit into dwarf society. It was part of what drove him down out of the mountains to meet other humans.
Unfortunately, as an outsider, they considered him strange and untrustworthy, so that even when he looked like everyone else, he still couldn't fit in. So he found the cracks between the two societies and learned to live on the fringe.
He began to feel used and torn. The humans wanted him to loot and pillage his dwarven heritage for their profit, and yet the only acceptance he could find in society seemed to be tethered to his past. Gradually, he came to the conclusion that no one truly cared about him or the lost ruins other than him. He began taking jobs to pay for his journeys, then using the journeys to liberate everything he could for himself. The dwarves cared more for their legends than their lost treasures, and the men only wanted money and power, so he gave them a taste of what they sought, and kept as much as he could. But for him, he developed an attitude that he was the guardian of a past that only he believed in. He became a one man museum.
Museum house artifacts, and that takes up space. Trensal found an unknown dwarven ruin that wasn't in any of the legends he'd heard as a child, and secured it for himself as an elaborate residence, and a monument to the heritage of his adopted race. As he began acquiring items in earnest, he took fewer jobs and started to become obsessed with treasure hunting.
One man always treated Ference with respect and understanding, and Ference, in turn, remained open to him when he sought help from the ranger. About a year ago, the man had come to Ference asking for a special recovery. He was a member of an ancient, secret society that sought to understand and study dragons. There were long standing rumors within the society of a particular magic weapon created by the dwarves that they wished to recover. They said little to him of what the item was (claiming that info was lost to legend), and carefully steered away from saying why they valued it so highly. He told Ference it had some connection to a dragon in its creation, and they wished to study it and keep it safe.
Ference was nobody's fool and wondered what the real purpose for recovering the item was, but he felt a connection to the man, and was willing to accept his offer. It also piqued his interest. Here was another legendary dwarven item that he had not heard about. He spent two months scouring dwarven archives at scattered settlements, and started to piece together the Legend of Rain Thana. He didn't see the connection to dragons, other than the dragon heart used in its creation, but that was someone else's politics, so he put those thoughts aside.
When he encountered our party earlier in the story, he was making his way to a meeting with a local dragon cult connected to the society he was working for. He had located the axe and tracked it to the area. Only after meeting you and recovering the axe did he realize the kobold dragon cult were the movers behind the whole recovery. He was able to escape them, but without the weapon, so he followed you as quickly as he was able, eventually catching back up with you outside Aron's Bowl.
Unsure of where your loyalties lie, and worried about his own, as well as those of the cultists, he has been waiting for an opportunity to relieve the party of the item and take it to the cult headquarters, which he has learned are on the slopes of the volcano west of the murky path ahead. He plans to deliver the item as contracted, and then to liberate it to his personal collection.
There is an opportunity to subdue Ference and reason with him, either to assist you with your quest, or to use the item himself rather than turn it over to anyone else. Ference is not an enemy to their quest, but he is extremely independent and self-confident. This makes him unwilling or unable to trust many, and given that the one friend he thought he could trust might be behind the dragon cult increases his anxiety.

Ference Trensal

Ference Trensal was an orphan taken in by a tribe of dwarves who rescued him from the ruins of a wagon train ambushed in a remote mountain pass. Unable to learn his true identity, and with no interest in spending time or money looking, they took him back to their home and raised him as one of themselves. This gave Ference an unusual interest and insight into the history and traditions of dwarves. When he became an adult, he left the dwarven city for the valleys of men to learn about his own heritage and culture. He was somewhat disillusioned by what he found and spent his time learning the ways of the wild, training as a ranger and border guard.
His knowledge of the hills and mountains of the wilderness made him a popular choice as a guide. After several years of this, though, Ference felt his soul wearing thin, and left the guides to seek his own adventure. With his knowledge of dwarven history and legend, he became obsessed with researching and locating anything and everything he could of lost dwarven artifacts - cities, towns, weapons, magic items, musical instruments, and jewelry, among others. He realized that with his training as a guide, his intimate knowledge of the mountains, and his ability to enter and commingle with human society gave him a better opportunity than most to track items down and recover them.
His reputation spread, and soon he found his services being retained to search for and recover specific items of interest to the powers retaining him.

I need to go to sleep... my mind is starting to drift. I'll continue this in the morning.

Revised Battle Axe description

Frost Battle Axe of Rain Thana
Battle Axe, very rare (requires attunement), sentient item

When you hit with an attack using this magic sword, the target takes an extra 1d6 cold damage. In addition, while you hold the sword, you have resistance to fire damage.
In freezing temperatures, the blade sheds bright light in a 10-foot radius and dim light for an additional 10 feet.
When you draw this weapon, you can extinguish all nonmagical flames within 30 feet of you. This property can be used no more than once per hour.

Additional Special Abilities:
Heart of the Dragon: The axe grants advantage to the wielder against fire-based attacks.

Eye of the Wizard: It also has the ability to cast two spells, Charm Person (level 2), and Sleet Storm (level 3).

Voice of Command: The axe gives the wielder command over the battlefield. It has 6 charges that can be used to give inspiration dice to the wielder’s allies in combat (this is similar to a fighter’s superiority dice). The wielder can expend one charge as a bonus action by giving a command directing an ally’s action in combat. The charge grants +1d6 to that ally’s attack roll on the action suggested, and must be used within one round of the command. If the target chooses not to take the direction, they must make a saving throw (DC15) or take 1d6 psychic/cold damage from resisting the power of the suggestion. The wielder can also make a command directing the opponent’s action as well, with them making a saving throw (DC15) to shrug off the suggestion, taking the 1d6 psychic/cold damage on a successful save. The axe regains 1d6 expended charges each morning at dawn.

Dragon’s Curse: A curse was placed on the axe by its creators that makes it vulnerable to dragon breath. If the wielder is caught in the breath weapon of a dragon, have them make a saving throw for the weapon (DC10). If the weapon fails its save, the weapon explodes in a icy burst of 3d8 cold damage.

Back to Work

I want to start out by revisiting the abilities of the frost battle axe. I think that what is there works well, but want to add a feature. My thinking is this: what about this magic item makes it more useful in a fight, particularly what makes it a tangible threat to a dragon, and what makes it desirable for dragon cultists?
As it is, it's useful against a red dragon because it is a glorified frost brand weapon. I tweaked it with a pair of spells and hamstrung it with a threat of destruction. But there isn't anything in the description as it stands that makes it particularly useful in a dragon fight, or all that threatening to the dragon's allies. So I'm adding a feature similar to superiority dice. The battle axe has 6 charges, and can use them as a bonus action to give inspiration to an ally in the form of a 1d6 bonus that can be added to attack rolls or ability checks.
This feature will give the wielder command over the battlefield, with the ability to direct attacks and influence them beneficially. I think this answers the charges I made above, giving the item a useful power that would be effective against a powerful ally by allowing one creature to guide the fight for all of their allies, and, as a result, would be considered with distaste by the dragon and the dragon cult. The threat to the dragon is more subtle, but I think it is still effective. The power of the wielder to direct attacks can coordinate a party's action in a big way (provided they choose wisely and the dice reward them).
I know that these types of inspiration often apply to other rolls, such as saving throws and ability checks, but I think those are out of line with the intent here. The weapon is granting the wielder a leadership role, and the ability to direct the fight, to direct attacks. I don't see them being able to anticipate a saving throw. Ability checks can have more leeway since the direction can be to take an action that might require one, like, "jump that chasm and attack it from behind." In that case, using the inspiration to ensure the success of the ability check feels justified.
I think another aspect to this that is becoming clearer is that the inspiration needs to be used in the round that it is given, and I think should also involve a literal direction (like the example above). In that way, the inspiration becomes like a Command spell, carrying the power of compulsion with it. Perhaps, that should be literal as well, with the target having the option of automatic success for allies, and the option of making a saving throw to shrug off the suggestion and act on their own. Doing this would cause them to take 1d6 psychic/cold damage.
The item recovers 1d6 expended charges each morning at dawn.
Now, we have an item worthy of a group of dragon cultists hiring a ranger to track down and destroy...