Finding the Horn
"Rythor wants to speak with me about the Mining Tunnel."
Go speak to Rythor, who is still in the Library. Rythor mentions the Tunnel that was being dug from the Bloodvein Mine into the Overgrown Spire.
"I completely forgot about the Tunnel Clarus Ovin promised to dig for me. Rythor is getting impatient. I better get back to Bloodvein Mine and see what's taking them so long."
Make your way back to the Bloodvein Mine, but enter it carefully. There are two Speckled Clannfear and one Speckled Daedroth in the room where the miners were, and another Speckled Daedroth and Speckled Clannfear in the room where there appeared to be another entrance on the minimap on your last visit.
The miners are all dead in the main room - and Squeaky's cage has been broken open, with Squeaky presumably eaten. When you approach Ovin's body, your quest log updates again.
"Clarus Ovin and all of his miners are dead, killed by creatures from inside the Tunnel they dug! I must neutralize the source of this threat."
In the south west room where the door appeared to be, there is now an actual door into Bloodvein Mine Side Tunnel. This is a small area with more Speckled Clannfear and Speckled Daedroth, as well as a number of gold veins, and a Miner's Crate containing Gold Nuggets, that leads to the Overgrown Spire Ruin. There are a number of what appear to be large roots in the area, presumably connected to whatever is covering the Spire itself.
The Overgrown Spire Ruin contains a lot of lava, and a number of places can only be reached by going through it. Make sure you are adequately prepared to do this.
"Picking up this ancient artefact, I feel it tremble in my hands. From within its sinister blade glows a divine radiance. I had better show it to Rythor."
You can now either exit the Ruin and return to the Guild, or finish clearing out the ruin and enter the Celestial Portal, or do the small side quest, The Sorcerer's Captive, detailed below.
In the Warlock Coffer, the notable items include a Warlock Hood, which provides the constant effects Fortify Health 25, Fortify Magicka 25, Frost Shield 10% and Resist Normal Weapons 10% all on self; a Warlock Robe, which gives the following constant effects, Fortify Health 90, Fortify Magicka 90, Frost Shield 40% and Resist Normal Weapons 20% all on self; another Warlock Glyph and a Warlock Enchanter. Similar to the Warlock Spellmaker, the Warlock Enchanter allows the creation of enchanted items like the Enchanters in the Arcane University and Frostcrag Spire and, like the Spellmaker, is also portable.
When you return to the Guild and speak to Rythor, he is somewhat angry with you as he specifically told you not to explore thr Ruin by yourself, and says that one day your impetuosness will get you killed.
When you show him the Horn of Zyyr, you may be given the choice to give Rythor the Horn immediately, in which case he thanks you and gives you his Pendant in exchange. Alternatively, your may be given the choice to refuse, saying that you are going to keep it. Rythor cannot believe that you actually intend in using a weapon like this, given its age, and says it must studied. You can then either say "Okay, but give me something in return" in which case he gives you his Pendant, or you can say "No way! I'm keeping it for myself" to which Rythor again offers you his Pendant in exchange for him keeping the Horn for now. No matter what, Rythor takes the Horn and gives you Rythor's Pendant in exchange, which has the following constant effects on self, Resist Paralysis 40%, Resist Poison 40%, Resist Shock 40%, Resist Disease 40%, Resist Fire 40% and Reflect Damage 5%.
Rythor now promotes you to Mentor, and, when asked about the Reward, gives you the key to Display Case D, on the first landing on the left hand staircase, which contains a Basilisk Talon.
When you ask Rythor again about the Horn, he says that he needs some time with it. When you ask him what you should do now he says you should speak to Aster Cei who has been asking for you for the quest The Revelation. Quest complete.
The glass from the pedastal next to the tunnel at the back and next to Display Case H containing a Bulging Vase has now been removed.
Verus will now sell you a Starmap and Sova now sells a Basilisk Poster.
"I've stumbled upon a frightened man held captive by an evil Sorcerer. I must find a way to unlock his gate and set him free."
If you speak to the man, Mavner, he will tell you he is being held by a captive by a Sorcerer who has been capturing people for years and experimenting on them or turning them into monsters. He begs you to find a way to free him, before he suffers the same fate.
This quest is just a small quest unconnected to the rest of the Guild quests, and irrelevant to that series. It basically offers up the opportunity to get a bunch of loot and a clue to the Malevolent Zinj.
Loot the lair of anything you want. As well as what's on the Sorcerer, there are three Human Hearts (very difficult to get hold of), quite a few ingredients including a fair amount of Mort Flesh, a complete set of Expert alchemical equipment and a lot of books. If you fancy stocking up on books, loot them all, although the most notable are the Destruction skill book The Art of War Magic, the Conjuration skill book The Warrior's Charge and the Alteration skill book Sithis.
Go through the door at the end, and there's a ladder down to the cell where Mavner is. Talk to him and he thanks you for saving him. He says the only thing he has to give you as a reward is the book Sentinels of Kar'toom, a valuable book unique to this plugin. If you read the book, you will see that it references the Zinj, one of which is in the lobby of the Guild. Mavner says the iron gate is stuck, so you will have to return back through the Dank Lair, and he says he will follow you. Quest complete.