So I'm running Dragon of Icespire Peak, right now I'm preparing Axeholm for a party of 6 level 6 PCs. Should be fairly easy for them. But as I'm preparing, I think I've noticed a discrepancy in just how many ghouls are infesting the fortress.

The guide clearly states that if the characters break down the gate, it makes a loud crash, attracting all the ghouls in the place to gather to the Mustering Hall. It also says that if the players clear out all of the ghouls in this encounter, they will not run into any more ghouls for the entire run of the dungeon. The guide describes the number of ghouls as being 3 ghouls plus 3 additional ghouls for each party member right? So 3 ghouls plus (3 ghouls x 6 party members = 18 ghouls) is 21 ghouls total, right?

But lets say that they don't alert the ghouls. Let's say one of the gnomes or the halfling rogue is able to slip through the arrow slits for the ballistae, and raises the gate without causing too much of a fuss. That means that the ghouls haven't gathered and are instead in each of their respective little groups spread around the dungeon. Let's go through these individual locations, shall we?

First area: The West Hall. According to the guide, there is (1) ghoul for each party member. 6 total ghouls. That one is easy. 

Next area: The Throne Room. This area is described as having (1) ghoul hiding behind the throne, who, when alerted, shrieks, alerting all ghouls in the ghoul bath area upstairs to crawl down the chimney and join the fray. This area has (2) soot-covered ghouls hiding in the chimney, plus (1) additional ghoul for each party member. So if my math is correct, that potential encounter is (1 ghoul behind the throne) + (2 soot-covered ghouls) + (1 ghoul per member so 6 ghouls total) = 9 ghouls. Add the West Hall's ghouls to that, we have 15 ghouls so far. 

Lastly, the Ghoul Den. This area is described as follows: "The stench of death and decay grows stronger as the characters approach this room, and they can hear the hisses and snarls of the ghouls that lair here. The room contains one ghoul plus one additional ghoul for each member of the party, not including sidekicks." 

...hol up

"The room contains one ghouls plus one additional ghoul for each member of the party." That means 7 ghouls total. But we already determined that there are already 15 ghouls elsewhere or otherwise defeated. So this means that there are, in fact, 22 ghouls total in Axeholm, not the 21 described in the Mustering Hall. 

Two possible scenarios.

1.) The ghoul behind the throne is said to have 40 hit points and be the source of the stench in the dungeon. It is very possible that he is not counted in the overall total that we were given in the mustering hall and instead be considered a miniboss, but that wouldn't make sense because according to the Mustering Hall, "The fortress contains three dwarf ghouls plus three additional ghouls for each character in the party, not including sidekicks. If these ghouls are killed here, the characters encounter no more of them in the fortress." 

2.) The much more likely scenario is that whoever designed this dungeon just missed one when calculating the total horde that gathers in the Mustering Hall. It happens. But I do think it's interesting and I wanted to point this out to any other DMs that are trying to prepare this particular quest.

I will probably just add a 22nd ghoul to the horde if they do break down the gates. They're level 6, after all, they can handle it. Hope this helps.

I’m actually surprised it’s not farther off.  I could easily see it written in such a way that bringing the whole place down on you at once is still a deadly, but winnable fight. Conversely, sneaking around would still need to be challenging if it’s worth stopping to roll initiative in so many rooms.  I didn’t do the math when I prepped it, but I just ran my 6th level group through there last week.  They didn’t break down the doors, but I had already adjusted the fights to include wraiths and ghasts in place of many of the ghouls.  (Less monsters to take turns with and more variety of threats.) I just used the DnDB encounter builder to give them a pretty deadly fight within the daily XP budget.  I also scaled up the other areas the same way.  Worked out great, actually.

Smart. I'm maintaining the number of ghouls, but I'm grouping them into swarms so three ghouls is a single unit with triple hp and 3 attacks. This also allows them to try to grapple a PC and knock them prone. Less initiatives, more attacks, I think it'll raise the tension nicely. It also means that our Paladin can feel like a badass by cleaving through 3 ghouls with just one swing, the sorcerer gets to feel more nukey, etc.