This mod has two components:
-A full set of artifacts for Gothren, to make him a much more dangerous foe. (It's yours if you can take it.)
-A dungeon that Gothren will banish you to, provided you make him angry enough. (Keep bothering him about being Horator.)

Artifacts:
(CE = Constant Effect)
-AoG_BonemoldBracerLeft: Resist Magicka 50 points for 10 seconds, Damage Int 10 points, Fort Enchant 15 for 10 seconds, Levitate 30 for 10 seconds on self
-AoG_BonemoldBracerRight: Resist Magicka 50 points for 10 seconds, Damage Str 10 points, Fort Enchant 15 for 10 seconds, Levitate 30 for 10 seconds on self
-AoG_BonemoldPauldronL: CE Fort Max Fat 50, Fort Max HP 25, Sanctuary 25, Reflect 25
-AoG_BonemoldPauldronR: CE Fort Max Fat 50, Fort Max HP 25, Sanctuary 25, Reflect 25
-AoG_BonemoldGah-julanCuirass: CE Restore Fat 5, Fort Max HP 25, Restore HP 5, Spell Absorb 25
-AoG_BonemoldGreaves: CE Restore Fat 5, Fort Max HP 25, Restore HP 5, Spell Absorb 25
-AoG_BonemoldBoots: CE Restore MP 1, Bound Spear, Fort Atk 25, Slowfall 1
-AoG_GothrenRingShock: 100 Lightning Shield 10 seconds on self, 50 Shock on target, Fort Enchant 15 for 10 seconds, Levitate 30 for 10 seconds on self
-AoG_GothrenRingFire: 100 Fire Shield 10 seconds on self, 50 Fire on target, Fort Enchant 15 for 10 seconds, Levitate 30 for 10 seconds on self
-AoG_ExquisiteAmuletEnch: 500 enchanting capacity            
-AoG_GothrenShirt: CE Fort Max MP x0.5, Fort Med Armor 25, Sanctuary 25, Spell Absorb 25
-AoG_GothrenBelt: CE Resist Magicka 25, Fort Med Armor 25, Fort Enchant 25, Reflect 25
-AoG_GothrenPants: CE Fort Max MP x0.5, Fort Med Armor 25, Sanctuary 25, Spell Absorb 25
-AoG_GothrenSkirt: CE Resist Magicka 25, Fort Med Armor 25, Restore MP 1, Fort Int 50

Upon entering combat, he will take off his robe and "throw" it at your feet and put on an adamantium helm. (He only does this if you did the dungeon.)

The dungeon:
Now when you speak to Gothren about becoming a Horator, he will get mad and if you bother him enough, he will banish you to the Mental Prison. You can use mark and recall to get out, but in the spirit of the mod, I'd like it if you tried to escape the old fashioned way.

If you have ever plundered the Telvanni vault in Vivec, then you will have an idea of how this dungeon works.
Each door you encounter will send you somewhere "random". And you will have to figure out which doors are the right ones to get out of the prison.
There are spectral Argonian guards that will attack you unprompted, so be ready for a fight.
You will find a set of floating notes above skeletons, as sort of mini diaries of the people who have been trapped here.

There is no treasure in the dungeon. It is a one time visit only place, so I didn't put anything in here.

Once you manage to escape the dungeon and you talk to Gothren again, he will fight you.

Technical notes:
Gothren's original Hortator dialogue has been edited so his disposition will fall and his fight will increase each time you speak to him. Once his fight hits 70, he will warp you to "Gothren's Mental Prison".
He will also hit you for 500 fatigue damage to simulate you being sent into a dream. It will take a few seconds for your character to get up.
When you leave the dream, you will get hit with another 500 fatigue penalty. Originally I wanted you to wake up directly in front of Gothren, but BCOM has him located slightly off center, so I had to put the spawn point a bit further back.
BCOM compatable.
Doesn't touch any existing cells.
The Argonians have 60 chameleon for the ghost effect (only visible in OMW, in vanilla, they look normal) and are set to self disable once killed. They have 80 fight, which will have them aggro you once you get close enough. They don't talk, they will just tell you to go back to sleep.
The ancestor ghosts have fight set to 0, so they wont bother you. They are just there for ambience.
Gothren's Mental Prison goes on "forever", I assume, if you wanted to keep going into the void one direction. You only need to stay in the "prison" area to find the solution.
If you want a hint, the doors with the little window bars are the "correct" path. I also put a dripping water sound near the "wrong" doors.
All the doors are "paired", so while it may seem like you're being thrown around in a chaotic fashion, you can always retrace your steps by going back through the door you came out of.

To playtest, you can do it two ways:

-Skip to the Hortator quest by using the console and entering:
Journal B7_GothrenHort 50
Then just talk to him and close the dialogue box again about four times to get him really mad. He will then send you into the prison realm.

-Increase his fight in the console by clicking on him and entering:
SetFight 70
Then talk to him and he will immediately send you into the prison.
You can also taunt him to increase his fight. You may need to bribe him a few times to get it to work properly.

Then find your way out by finding the right door in the maze or skip the puzzle:
coc, "Tel Aruhn, Upper Tower"
Then talk to Gothren again to immediately start a fight.

Once you beat him, you can take his artifacts. Enjoy!

Tested on OMW and vanilla.

Update v1.1
Added ModFight 10 to his Telvanni Hortator dialogue options, allowing the banishment to trigger at Journal B7_GothrenHort 30. Originally only did it when greeting at Journal B7_GothrenHort 50. Should allow for banishment more easily.