So I've been struggling with preparing chapter 9 and 10, solely because Pandemonium is such a cool area and the book just completely ignores most of it. This has led to deadline problems and I didn't have time to prepare the Ruinous Citadel properly. Ofcourse my party immediately beelines towards the citadel, so I had to do some winging it. The first part wasn't really the problem, but I wanna paint a picture so I'll tell what happened.
They sneaked in through the food room, and alerted the two guards in Y2 by opening the door. They banished the demons back to the Abyss, but when the Raklupis in Y5 heard spells being cast, he telepathically told all the Kakkuu spiders to investigate, keeping an eye on the door. The party tried to sneak out with Naxa after finding her, but when an invisible character got spotted by the Raklupis' True Sight, the fight went down. They banished the Raklupis, so I had it that the final Raklupis and Phisarazu spyder-fiends from Y7 would join the fight after 2 rounds to command the 11 Kakkuu fiends.
The fight became a big game of strategy, walls were cast, measuring was done, and after two rounds the last remaining spyder-fiends joined the fight. No real damage was done as the party had used the Cube of Force they got in chapter 3 to protect themselves from anyone entering, and the Kakkuu fiends were simply too many with lots of resistances and good rolls to easily do damage to. After 3 more rounds the Order of Scribes Wizard put their spellbook in Miska's chamber, and that's where my tiredness changed some things.
I narrated Miska trying to break through the portal as written. Then being unprepared I quickly searched for more information on Miska and found the statblock from bettermonsters: https://www.reddit.com/r/bettermonsters/comments/1nomvc7/complete\_miska\_the\_wolf\_spider\_a\_prince\_of\_demons. In it is described what a character can do to pull the Rod out of the seal, but I misunderstood and let Miska roll in that manner. I told the players Miska needed to roll a cumulative of DC70 while ignoring anything under a 25, and when Miska rolled a 37 on his first turn the players were SCARED. All the players had to do to pull out the rod was succeed on a DC25 athletics check, but none of the players had a high strength to pull it off. They immediately started Shapechanging and True Polymorphing to get the best monsters to pull the rod out, but kept rolling low. When Miska needed a roll of 27 to break free, I rolled a 26. Then they used the Power of Secrets to gain advantage, and the warlock managed to pull out the Rod. Bam, fight over, everyone goes home, they won.
The fight began at the end of the session, and I kept thinking "oh sure let's do a little more and they'll run" or "okay let's see what they're going to do". The session took 11 hours in the end, and even though I was BROKEN, it was so worth it.