Lots of Questions!

[Zersetzor]

Hi, I just (almost) finished my first run through this great map solo. Almost, because I couldn't hope to beat the final boss, even though I played on easy mode, but that's fine since the map is supposed to be played in a group of three.
While I greatly enjoyed the whole game, I couldn't for the life of me find out some things, even after thoroughly scouring the map up and down, checking every bookshelf, ghost and blue circle, and using the map reveal code. Answers or hints to any of these would be greatly appreciated, and I expect some of them will be linked.
1. What is up with the circles of power west of the Zultar forest dungeon? No way of interacting with them seems to do anything.
2. In the centre of the map, north of the horde base, there is a circle of power that summons a Guardian when one steps into it. I seem to recall two different Guardians in two different runs, but I found no way of getting more than one in the same run.
3. What determines when a demon will spawn on top of the hero? Is it somehow linked to idle time?
4. I was playing Hunter, and the options Mastery and Pet Damage Increase in the stats menu seemed to have the same effect (1.5% damage increase for summons), only that there are some positive interactions with skilling Mastery. Am I missing something here or is that just an artifact of balancing classes?
5. There is a skeleton Orc hidden behind a volcano early on in the map. If one inspects the circle in front of him, there appears a cryptic description of his sad state. His name is Gar'thok and he holds his own custom axe. I found no meaningful way of interacting with him, but I have a hunch that he has something to do with the "throne" like area a bit to the east, as inspecting it prompts text about this being the seat of some high-ranking military official.
6. (This one I'm actually quite sure about) The Sphere of Darkness starts a quest to bring it to the Dreadlord in the Vault. I found no way of finishing this quest as a hunter, and the Dreadlord claims that only a Deathknight could help him, so I'm guessing this is simply the case?
7. Somewhat off the path towards the Park area, there are four differently coloured runes on the floor, labeled rune of Tempest, Yew, Power, and Flame. I found no way of interacting with them that had any noticeable effect, and I didn't find any hint towards a code or something like that. At first I thought they might prompt different Guardians to spawn, but that didn't seem to be the case.
8. There is a Tome of Experience located next to a pit of spikes, but the only narrow path that leads to it is an instant death trap. Similarly, later in the map, there is a Chest Key in a Stonehenge-like structure, with all the paths between the stones being death traps. Are these two simply booby traps? Or is there some way to get to the respective items?
9. There is an area called the "Vault of Titans" that can only be accessed with a special item. I'm guessing this item is the "Titan Handle" that can be seen earlier in the dungeon. But the only way to the handle seems to be booby trapped with a sort of fire pit/ trap. I tried getting past it with an item that lets one pass fire in another instance and with invulnerability, but neither worked. What am I missing here?
10. I found all of the 23 secret areas, except for this one: https://www.hiveworkshop.com/attachments/16-jpg.282260/ the location seems to be completely isolated from the rest of the map, and is directly east of the spider boss room. I thought one could use the cave that seems to go into the separating wall from either side, but that didn't work. Then I noticed a statue in the room with the secret that had electric sparks jumping around it, but I could not find a corresponding statue anywhere in the rest of the dungeon. How do I get there?
11. Not far from the spider boss there is an area call the "Master's Chambers" (or something like that). It features two doors that are to be opened by the dragon aspects and the "rarest key" respectively. I did find the "Token of Ysera", and its description says that there is also a "Token of Nozdormu", but I could never locate it anywhere. As for the "rarest" key, the closest I came wer the Ghost and Eilric's (the former king) key, but neither of them worked and both of them had uses elsewhere.
12. In the treasure room area there is a skeleton warlord who says that "only endless fire" can save him. I thought this would be an allusion to the "Eternal Fire" item one can get from the quest in the waterworks, but using it on him, putting it in front of him, and even selling it to him did anything. I'm guessing there is some other item that I need here, but I checked pretty much every fire source I could find, all to no avail.
13 In the Vault one can find the "Mysterious Wanderer" npc, behind a blocked door. The information of the door says (like some others in the area) that some mechanism would open it. I managed to assemble the rubies, and revive the dead tree in the vault, but neither event opened this gate, and I could not find any other opportunity for an event or trigger.
14. In the south west of the sunken city, there is an Anvil, next to what seems to be some fire pit for disposing of bodies. I could not find any use for either of the two, and have no idea which item might be needed to make use of them.
15. There exists an item called the "Ultrasafe Transporter". Its description states it would transport the user to a random point on the map, but with no guarantee of success. After a number of uses I had not a single success. Is there some trick to it, or am I just unlucky?

Thanks in advance for any answers!

edit I found the mushroom

 

[SpasMaster]

1. What is up with the circles of power west of the Zultar forest dungeon? No way of interacting with them seems to do anything.

There is a pattern of 4 colors that needs to be achieved. Perhaps you've seen that patter elsewhere on the map already?

I seem to recall two different Guardians in two different runs, but I found no way of getting more than one in the same run.

You can't get them all together. There are certain elements of the map that are unique to each run to provide replayability.

What determines when a demon will spawn on top of the hero? Is it somehow linked to idle time?

It's entirely random.

I was playing Hunter, and the options Mastery and Pet Damage Increase in the stats menu seemed to have the same effect (1.5% damage increase for summons), only that there are some positive interactions with skilling Mastery. Am I missing something here or is that just an artifact of balancing classes?

You are not missing anything, it just ended up like this during development. It will be looked at in the future.

There is a skeleton Orc hidden behind a volcano early on in the map. If one inspects the circle in front of him, there appears a cryptic description of his sad state. His name is Gar'thok and he holds his own custom axe. I found no meaningful way of interacting with him, but I have a hunch that he has something to do with the "throne" like area a bit to the east, as inspecting it prompts text about this being the seat of some high-ranking military official.

He is an Easter Egg and cannot be interacted with. Good try with the Throne tho, I like it.

The Sphere of Darkness starts a quest to bring it to the Dreadlord in the Vault. I found no way of finishing this quest as a hunter, and the Dreadlord claims that only a Deathknight could help him, so I'm guessing this is simply the case?

You just need to be a Death Knight.

Somewhat off the path towards the Park area, there are four differently coloured runes on the floor, labeled rune of Tempest, Yew, Power, and Flame. I found no way of interacting with them that had any noticeable effect, and I didn't find any hint towards a code or something like that. At first I thought they might prompt different Guardians to spawn, but that didn't seem to be the case.

They can be interacted with and it will be obvious to you when you get one object. But first you need to solve another puzzle.

There is a Tome of Experience located next to a pit of spikes, but the only narrow path that leads to it is an instant death trap. Similarly, later in the map, there is a Chest Key in a Stonehenge-like structure, with all the paths between the stones being death traps. Are these two simply booby traps? Or is there some way to get to the respective items?

Simply death traps.

There is an area called the "Vault of Titans" that can only be accessed with a special item. I'm guessing this item is the "Titan Handle" that can be seen earlier in the dungeon. But the only way to the handle seems to be booby trapped with a sort of fire pit/ trap. I tried getting past it with an item that lets one pass fire in another instance and with invulnerability, but neither worked. What am I missing here?

There is an item that drops from the Firelord boss that allows you to walk over the fire pit/trap. The Handle, however, is just one component needed to assemble the item that would open the Vault of the Titans.

I found all of the 23 secret areas, except for this one: https://www.hiveworkshop.com/attachments/16-jpg.282260/ the location seems to be completely isolated from the rest of the map, and is directly east of the spider boss room. I thought one could use the cave that seems to go into the separating wall from either side, but that didn't work. Then I noticed a statue in the room with the secret that had electric sparks jumping around it, but I could not find a corresponding statue anywhere in the rest of the dungeon. How do I get there?

In close proximity to the Zultar Forest dungeon there is a well hidden item (you need to look carefully) that would allow you to go through the cave.

Not far from the spider boss there is an area call the "Master's Chambers" (or something like that). It features two doors that are to be opened by the dragon aspects and the "rarest key" respectively. I did find the "Token of Ysera", and its description says that there is also a "Token of Nozdormu", but I could never locate it anywhere. As for the "rarest" key, the closest I came wer the Ghost and Eilric's (the former king) key, but neither of them worked and both of them had uses elsewhere.

Acquiring the rarest key and the two tokens at the same time are heavily RNG-dependend and therefore not obtainable in every game. You just need to be lucky with the drops.

In the treasure room area there is a skeleton warlord who says that "only endless fire" can save him. I thought this would be an allusion to the "Eternal Fire" item one can get from the quest in the waterworks, but using it on him, putting it in front of him, and even selling it to him did anything. I'm guessing there is some other item that I need here, but I checked pretty much every fire source I could find, all to no avail.

One of the puzzles (that you've already asked about) will help you interact with him.

In the central Horde camp, there is a shop that offers a recipe using four rare ingredients. I found three of them, but could not locate the "Karrata Mushroom", even after inspecting every mushroom I could find on the map.

It's on the ground near the Gar'thul bossfight (The Chaos Orc Warlock).

In the Vault one can find the "Mysterious Wanderer" npc, behind a blocked door. The information of the door says (like some others in the area) that some mechanism would open it. I managed to assemble the rubies, and revive the dead tree in the vault, but neither event opened this gate, and I could not find any other opportunity for an event or trigger.

There is a well hidden lever in very close proximity to the door. You just have to figure out how to see it. Your view to it might be obstructed in a similar way as the rubies were hidden.

In the south west of the sunken city, there is an Anvil, next to what seems to be some fire pit for disposing of bodies. I could not find any use for either of the two, and have no idea which item might be needed to make use of them.

The Titan Vault, the Elixir with rare component and the Mysterious Wanderer will eventually lead you there. No point thinking about the anvil without first figuring those other things.

There exists an item called the "Ultrasafe Transporter". Its description states it would transport the user to a random point on the map, but with no guarantee of success. After a number of uses I had not a single success. Is there some trick to it, or am I just unlucky?

That's surprising. You must be very, very unlucky. If it continues not teleporting you, there might be a bug involved.

 

[Zersetzor]

Thanks for the answers, I managed to get most of the stuff done now. To be honest, I was sure to have tried some of the things before, but must have misremembered. There's two things I still couldn't figure out yet though. After releasing the Skeleton from the treasure room, he gives you a vial of King's Blood. I have no idea what to do with that. And when trying to use the Titan Handle and the Elixir at the Anvil it says I am still missing something. Since the quest talks about a Titan's Hammer, I'm guessing it is some sort of stone, or head (as in hammer head), no idea where I might have missed that one.