I have a player who is a necromancer and insists on always keeping their risen dead "concealed" by use of large cloaks and masks.
Generally, this includes 4 skeletons and 4 zombies. The PC is very certain that if they took the time to scrape every ounce of flesh from the zombie's bones that they will become odorless. A long while back, I gave this some thought and decided to allow it, lowering the stats of each zombie (primarily their hit dice). As the game has progressed, this PC wishes to now pad the 8 undead minions with some clothing to reduce noise of clattering bones, throw large cloaks on them to hide everything, and furthermore puts masks on each one to hide their faces and claims that no one will notice or care.
So basically, this PC has 8 cloaked "bodyguards" with masks who can't speak or respond to anyone else, shy of being attacked. The longer this goes on, the more silly it becomes, walking into libraries with an entire host of undead cloaked figures with masks, having them wait in rooms or areas during lengthy social engagements, etc.
This PC is one of those power players who insists on a lot of far fetched theories and ideas that are always requiring me (the DM) to come up with possible scenarios or solutions based on these – while not wanting to say no to everything unless it's unreasonable to me. I don't mind this method of disguising undead minions in certain areas of the game, but some of the other players are starting to complain and I'd like to nip this in the bud and find a solution everyone is happy with before it gets too out of hand.
Is there a way to have NPCs react to this or have some kind of checks/saving throws to discourage this kind of behavior?
In this homebrew world, magic is rare and generally frowned upon by most people – as they are ignorant of it and generally fear it. Undead are not a common thing and are typically associated with evil if a populace has even ever encountered such a thing. The fallout from the undead being discovered would be rather large and potentially ruin the reputation the party is trying to build with the region they are in. Suspicious guards and the occasional person may ask them, but perhaps there is a better answer that I'm not thinking of that directly involves this not working due to their undead states or something. I don't want to flat-out say that the PC can't do this, but I generally forget about them when the party is in a city or somewhere that, if these were found out, would cause a lot of interesting issues, to say the least.
Best Answer
Dan B raises a good point - having your PC's undead troupe called out and identified is likely only going to cause issues.
However, if you have a way of controlling this - perhaps when they do get caught out, the guards issue him with a warning "Hey guy, we know you're in charge of these things, but we can't just trust you to keep them in line. You sneeze the wrong way and they might jump little ol' granny over there. Next time we won't be so lenient"; to catch them out, you can take some inspiration from the Monster Manual:
As you explained, they have dealt with the apparel and the smell, but the way they move is still identifiable. These are half-dead creatures that do not have full control of their motor skills.
Even if they are controlled by the Necromancer, that does not make them smarter. They will still act in this manner when instructed to "get them!" If they're on the second floor of a tavern, and their target is below them, they will still clatter straight over the balcony - the shortest, straightest path. For the Necromancer to make them somewhat believably smart in their decisions, he would have to micro-manage them - even when walking through crowds. This mob of shambling bodyguards would simply bump into stalls and completely ignore passers-by as obstacles. A crowded street would be hell for him and his posse.
In all honesty, this isn't a bad thing. You could certainly have fun with it. Perhaps describe the chaos that these jerky, dorky and dumb zombies are clattering around, bumping into everything and causing chaos, perhaps making the Necromancer feel somewhat responsible for the posse, like a nanny with a group of toddlers; "Oh sorry about that! Jeffrey is still learning to walk straight! Apologies! Anthony lost his feet last night and still hasn't reattached them properly!"
My only other argument is that the type of magic that keeps a skeleton in one piece is different to the magic that simply brings life into a rotting corpse - flaying the zombie is not upholding the magic that keeps a skeleton together.