The Elder Scrolls IV: Oblivion Guide - Shivering Isles
Quest 10: Ritual of Mania
Speak to Sheogorath in Sacellum Arden-Sul once you've made your choice. First, you must acquire some Greenmote. Wide-Eye the Argonian can help you; she can most likely be found wandering around the House of Mania. Go to the House of Mania at around 9:00AM. Select the 'Thadon' dialogue option while speaking to Wide-Eye to learn that all of the Greenmote is stored in the Greenmote Silo. She refuses to disclose the location of this silo, so it looks like you'll have to do a bit of snooping.
Wide-Eye mentioned that she does a 'special errand' every day at 12:00PM. Have 'Ritual of Mania' set as your active quest to keep track of Wide-Eye. If it isn't yet 12:00PM, use the wait menu to pass as many hours as necessary to advance the time to around 11:00AM. At this time, enter the Halcyon Conservatory area. Wide-Eye should be there already, most likely seated next to Thadon. At 12:00PM, Wide-Eye will get up and leave the conservatory. Follow her to the Palace Grounds area. Once you reach the spot, you will witness Wide-Eye activating the secret entrance to the Greenmote Silo.
Follow Wide-Eye at 12:00PM to discover the secret location of the Greenmote Silo.
After Wide-Eye has entered the Greenmote Silo, follow her in. It would be a good idea to create a separate save file at this point, just in case something goes wrong. If you have Autosave enabled, you can simply reload the Autosave filed that is created when you first enter the silo.
There are Golden Saints in the Greenmote Silo, so take your time as you must not be seen! Turn left at the first split; by going this way, you should be able to avoid the troop of Saints entirely and still catch up to Wide-Eye when the paths intercept. Keep to the shadows; if you are forced to follow Wide-Eye over lighted area, let her get a bit ahead of you before continuing the pursuit. When you reach the hill overlooking the entrance to the silo, allow Wide-Eye to enter.
You must enter the silo and grab some Greenmote while Wide-Eye is not looking. This may prove difficult. When you first enter, peek around the corner to see if Wide-Eye is standing there (she will hopefully have her back to you). If she is, move around to the opposite side of the Greenmote stash, take at least two Greenmote into your inventory, and then slowly make your way out of the silo. Once you have the Greenmote, you're pretty much home free. If you are spotted by a Golden Saint on your way out, she will likely not do anything more than inform you that the area is off-limits.
Acquiring the Greenmote.
Now that you have the two portions of Greenmote, you must plant them in Thadon's evening meal and wine. You must add the Greenmote to his food before he has his dinner. If you miss your opportunity, you will have to wait and try again tomorrow. Thadon's dinner is prepared in the Duke's Quarters, which can be accessed from the Halcyon Conservatory in the House of Mania. Of course, entering these quarters is considered trespassing, so you must unlock the door without being witnessed. Ensure that Sneak Mode is enabled and that the sneak icon is faded before picking the lock on the door to break in.
If your character is not big on stealth, you might have a tough time planting the Greenmote in Thadon's dinner. If your character's Sneak skill level is quite low, remove any heavy armour that is equipped and replace them with any piece of equipment that fortifies the Sneak skill (such as the Raiment of Intrigue). A Chameleon or Invisibility spell or scroll would also help. It's also quite dark in the Duke's Quarters and you won't be able to use a Torch. Create a Ring of Nighteye if you are able to, or get your hands on some Nighteye potions or a spell. Of course, if you must prepare in this way, you'll have to wait to plant the Greenmote another day. If you are unable to progress due to your character's low Sneak skill level, at least you have options.
Sneak into the kitchen in the Duke's Quarters and plant some Greenmote in Thadon's Meal and Thadon's Wine before his evening meal at 8:00PM.
With 'Ritual of Mania' set as your active quest, an arrow on your compass will point to the wine and food. Upon entering the Dukes Quarters, move forward and then turn left. At the end of this room is the entrance to the kitchen. Hide in the alcove behind the wine barrel to your right just before the entrance to the kitchen. There are two Golden Saints that walk up and down this area; wait until one of them has passed by the wine barrel you are hiding behind, and then creep into the kitchen. At this point, another Golden Saint will be coming up the hall. If you are quick enough, you should be able to make it into the kitchen without being spotted.
Once in the kitchen, place the Greenmote in Thadon's meal and wine (on the second shelf of the cabinet that's to the left of the food table). If you are having trouble sneaking past the Golden Saints, as long as you aren't carrying any stolen items you wish to keep, you could always try making a run for it; slip the Greenmote into the food and wine, and then pay the gold fine for trespassing. If that's how you wish to go about it, consider leaving any stolen goods you are carrying on the ground outside of the Duke's Quarters.
After planting the Greenmote in Thadon's evening meal, make your way to the House of Mania. Dinner begins at 8:00PM, so use the wait menu to pass as many hours as necessary to make it that time. Then, take a seat and watch the show. When the Duke collapses, search his corpse to receive a vial of Thadon's Blood. Search again, and you can take the Diadem of Euphoria hat that he was wearing.
Planting the stolen Greenmote in Thadon's evening meal
With Thadon's Blood in your inventory, return to Sacellum Arden-Su. Approach and activate the Altar of Arden- Sul. There, speak to Sheogorath afterwards. After the small scene that ensues, speak to Sheogorath again to receive the Ring of Lordship. This ring adds the Resist Disease and Shield effects, and fortifies the Personality attribute.