Hi! I'm running the Sunless Citadel in 2 weeks. My group is 5th level so I have exchanged most of the monsters for more powerful ones while trying to keep most monster types either similar or in keeping with the theme of the adventure (for example, the goblins have been switched to hobgoblins, twig blights to vine blights, Guthash and the giant rats to a ghast and some ghouls, etc.). Any tips for running the adventure?

Use passive perception on the secret doors, if they miss them too bad. If the hobgoblins are alerted set up some traps. Have the monsters be a little more active and set up patrols. 

Quote from jasperrdm >>

Use passive perception on the secret doors, if they miss them too bad. If the hobgoblins are alerted set up some traps. Have the monsters be a little more active and set up patrols. 

 Thanks!

For whatever it's worth, I did a modified version of this a while ago and found it helpful to make an isometric map to see how all the levels fit together in my head.  I think it would be even more important to see the whole sinkhole at once if you have 5th level characters with potential fly spells, et al.  If it helps at all, here's what I made one weekend in quarantine:

Level 5 will need a lot of scaling up compared to the level 1-2 design for the dungeon. You will need to really beef up the kobolds and goblins to make them a credible threat to a level 5 group.

One aspect of the dungeon I liked was that it did not require the characters to kill everything. They could be diplomatic with the kobolds, rescue the dragon and have some help eliminating the goblins. At level 5 this might not be needed but it still might be a fun way to proceed with the module.

Quote from TimCurtin >>

For whatever it's worth, I did a modified version of this a while ago and found it helpful to make an isometric map to see how all the levels fit together in my head.  I think it would be even more important to see the whole sinkhole at once if you have 5th level characters with potential fly spells, et al.  If it helps at all, here's what I made one weekend in quarantine:

 Wow, that map is really cool! It will definitely help a lot. Thanks a lot!

Quote from David42 >>

Level 5 will need a lot of scaling up compared to the level 1-2 design for the dungeon. You will need to really beef up the kobolds and goblins to make them a credible threat to a level 5 group.

One aspect of the dungeon I liked was that it did not require the characters to kill everything. They could be diplomatic with the kobolds, rescue the dragon and have some help eliminating the goblins. At level 5 this might not be needed but it still might be a fun way to proceed with the module.

 

 Thanks for answering! I’ve swapped the goblins for hobgoblins so that they will provide a decent challenge for the group. I strongly suspect they won’t want to fight the kobolds, but I’ve still boosted them up a bit in case the PCs decide to go murder-hobo on them. 

I'd use Needle Brights rather than Vine Blights (10ft movement stinks in a fight). Also if the final battle is underwhelming, consider having the Tree become a Treeblight after Balek dies. Have him be absorbed by the roots and his face on the tree as it cries out in his voice.

One more thing, Give Meepo some pc levels or make him a Master Thief. One of my cold open for the module was a lone kobold with a stop sign blocking the road. The toll was not money but ropes, poles, pick axes or other construction gear because the kobolds were trying to widen the valley and raise the castle. 

Quote from Whiskeyjack8044 >>

I'd use Needle Brights rather than Vine Blights (10ft movement stinks in a fight). Also if the final battle is underwhelming, consider having the Tree become a Treeblight after Balek dies. Have him be absorbed by the roots and his face on the tree as it cries out in his voice.

Having Belak be absorbed by the Tree when he dies is a really good idea! I’m definitely going to use that. I’ve actually decided to use all three types of Blights instead of just one, mainly because it’ll be more fun for the players then just fighting all one type of blight over and over again, and also the Nolzur’s minis line doesn’t sell individual blight packs; if you want one, you get the other 2 as well, so I feel it would be a waste to not use them. 

Quote from jasperrdm >>

One more thing, Give Meepo some pc levels or make him a Master Thief. One of my cold open for the module was a lone kobold with a stop sign blocking the road. The toll was not money but ropes, poles, pick axes or other construction gear because the kobolds were trying to widen the valley and raise the castle. 

 Thanks for the suggestions! I’m thinking of make Meepo a Kobold Inventor with 2 levels of rogue, so that he won’t get killed in every fight the party gets into.