So, some quick background on my situation. I have a group that is currently exploring Undermountain through the Dungeon of the Mad Mage adventure. Its a pretty eclectic group, but the adventuring party is sort of built around a trio of players whose characters are siblings with an older sister and a brother/sister pair of twins. The group, as a whole, have been torching their way through the first couple of levels of the dungeon, slaughtering any Xanathar outposts they come across pretty vigorously and mostly becoming a pretty pointed thorn in the organization's side. A lot of this is led by the twin brother, as he joined up with the Zhentarim during the Dragon Heist adventure and the party sort of collectively internalized the Zhent/Xanathar struggle, even though I had not used Xanathar as the main villain of that previous adventure.

Anyway, long story shorter, when the party crossed paths with the Zhentarim drow, Rizzeryl, and his wererat band on floor two, they agreed to help him wipe out the last Xanathar guild outpost, Spider Eyes Watch Post, on the northern part of the level as they had already destroyed the Dead Eyes Watch Post. The party decided to find a place to rest for the night as they were running low on combat resources, but the twin brother character wandered off to fight the outpost on his own and was initially "captured." It turns out, after talking with him after the game, he basically had to drop out due to some IRL issues and was hoping I would kill his character.

So, with that knowledge, I plan to do just that. I have decided that the Xanathar Guild has had quite enough of these jerks coming in and killing all their outposts. As a "lesson" they are going to use their contacts and guild resources to "distribute" parts of the twin brother across various deeper floors (a hand here, a rib-cage there, a heart there, a head there, etc.) along with playfully cruel notes suggesting where the party might find the next piece. This is sort of important as the party doesn't have access to magic that would bring someone back to life without a mostly intact body, an even if they did manage that little bit, it wouldn't work until much later anyway as I have a home picked out already for his soul. Of course, this sort of plan by Xanathar to either scare the party out of the dungeon or wear them down through the attrition of the lower levels is likely to backfire, as the rest of the party are, well, adventurers.

All of that backstory aside, what I need are some suggestions or ideas for how and where to distribute body parts, as well as maybe clever little notes taunting them deeper into the dungeon.

To start things off, at Spider Eyes Watch Post, the party will find both of the brother's hands splayed out in a box with one of his eyes in the center, creating a grisly image of the Xanathar Guild logo. There will be a cruel note taunting them and hinting that they will find more in Skullport (and they will find another piece along with another note in the abandoned drow spider house that shadows the underground city). But what will they find, and where will it point them next?

They find his head, poorly sewn onto the neck of one of Olive Stillwater's zombies. She refuses to give it unless they buy it, and when they try and lead it anywhere, the stitches come undone, and the head topples off. In the neck is a slip of paper with their next clue(working on that now). When this happens, Olive cackles and says "No refunds!"

(I know you said the drow place, but I thought this would be more interesting, and certainly more macabre)

The next piece is at floor 4 in the zhurkwood grove. The players must chase around animated barrelstalks to find the piece. One of the dozen or so barrelstalks is filled with blood, rather than water, and inside is the heart of their friend, floating in the bloody water.

Both of those sound interesting.

Not sure where to put something in Wyllowwood, as the Druid would probably not take kindly to the Xanathar Guild's intrusion, and there are many beasts which would happily devour the parts. Possibly one of the dolls hanging among the trees is actually made up of little scraps of him, parts that were not used for anything else. That way any part that wasn't taken care of would just be there.

Also, it doesn't have to be every floor. I plan on seeding them where it would seem appropriate. Places that have Xanathar Guild or Drow influences. Also areas where it might be creepy. He was a shadow sorcerer, so part of him might be traded away to the shadow dragon on floor 17. I was thinking of having one of the big liches on a deeper floor have his soul.

I just realized this, a problem with the whole hunt. The adventurers will definitely need more than 10 days to find all the parts, and raise dead, the lowest level spell that can return someone to life, but requires all their body parts, and has a longer timespan that 1 minute, cannot resurrect anyone who has been dead for more than ten days. Resurrection, the next lowest which has a long enough time limit allows you to resurrect someone if you just have one piece of their body. If they were delving all the way down to level 20 to take back the soul from Ezzat would definitely be able to cast that spell, unless there were no clerics(in that case this doesn't matter)

The party doesn't have a Cleric (just a Bard and a Druid for healing), and without the soul, any Resurrection spell is going to come back empty. Also, it will likely be more of a personal thing by that point as well, choosing to collect all the pieces to get their brother's body back in one piece and not leave him scattered across a mega dungeon.