I'm trying to set up an ambush in a tower where there are ghosts or some creature like them that has the ability to walk through walls.

If I had a room 20 feet by 20 feet and a party of 5 Medium-sized PCs, both doors secured with them in the room, how many ghosts could I hide in the walls?

This door opens into another room that's enormous, but this room specifically would be magically sealed so that the PCs wouldn't be able to get out until the required number of monsters were defeated. I'm just trying to figure out how many ghosts could be in the walls so that way I could figure out how many to put into each wave.

The party consists of five 6th-level PCs: 1 barbarian, 1 monk, 1 paladin, a cleric and an elemental wizard.

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    \$\begingroup\$ A group of Ghosts specifically is likely to be really unfun unless your party gets lucky with saves against Possession. Having half your party fight the other half to the death is less than enjoyable. I'd consider using Specters or Poltergeists instead, they don't remove entire players from the fight on a failed save. \$\endgroup\$
    – Erik
    Mar 29, 2022 at 7:28
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    \$\begingroup\$ If this is specifically a tower, can there be ghosts in the floor and ceiling as well? Or do they only enter through the walls? \$\endgroup\$
    – Kirt
    Mar 29, 2022 at 16:39
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    \$\begingroup\$ Be cautious using ghosts against characters below 10th level, especially multiple ghosts. Their horrifying visage attack can potentially age a character into old age if the dice fall wrong, and they only have one day to get a 5th level spell to undo that. Even if it doesn't risk killing or forcibly retiring a character through sheer age, a lot of people feel a strong connection to their characters and wouldn't take well to having 40 years suddenly added to their age. If you're going to do this, I'd strongly recommend having a nearby means of getting the necessary undos. \$\endgroup\$ Mar 29, 2022 at 19:16
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    \$\begingroup\$ Presumably way more than enough that the party is screwed unless the cleric and paladin get very lucky with possession saves and Turn Undead, if they all come in at once. \$\endgroup\$ Mar 30, 2022 at 7:47
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    \$\begingroup\$ Are you looking for answers about exactly how many ghosts could physically fit in the walls? Or how many ghosts you should pit against the party? \$\endgroup\$ Mar 30, 2022 at 14:27

2 Answers 2


None, or Unlimited

A ghost takes 1d10 force damage every time it ends its turn inside an object. If the ghosts are literally waiting in the walls, they're going to be destroyed in a bit less than a minute.

On the other hand, the ghosts could simply be waiting outside the room. (Or, if you're feeling fancy, they could wait on the ethereal plane.) If you're willing to allow this, then your question becomes "how many creatures can be waiting outside a room?" and of course the answer is unlimited. (They could stand in an arbitrarily long line, for example.)

But your xp budget only goes to four at once

I went to Kobold Fight Club and told it that you had a group of five level-six characters, and I started adding ghosts to the encounter. After the fourth ghost, it told me that the encounter was "deadly" difficulty (8800 adjusted xp, where the "deadly" threshold is 7000xp). If you have more than that at once, you risk killing your adventurers.

Your daily budget is 20000xp, and you could reach that with three groups of three ghosts each.

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    \$\begingroup\$ Can you elaborate on what "a very large number" means? Is it a smaller than infinite amount? \$\endgroup\$ Mar 29, 2022 at 14:00
  • \$\begingroup\$ You could have hollow walls to get around the ghosts taking damage. Or there could be a narrow corridor more or less surrounding the room which the ghosts are hiding inside. \$\endgroup\$ Mar 30, 2022 at 3:26

Well, ghosts are medium creatures which means that they can squeeze into a small space, unfortunately medium creatures in 5e effectively can't squeeze, so you are limited to one ghost per 5' x 5' section of wall.

If you have a 20' x 20' room with 5' thick walls then you have 20 sections of 5' x 5' wall - four on each side plus one in each corner.

However remember that ghosts can use Etherealness to go to the ethereal plane. That means you can hide an additional 20 ghosts in the ethereal plane in those same parts of the walls. Just remember that for the ghosts in the material plane if they end their turn in the wall they will take damage as per Incorporeal Movement.

I would suggest not worrying about it, and having all the ghosts located outside the room in the ethereal plane. As they are needed have them use Etherealness to shift to the material plane, then enter the room by phasing through the walls. If you want them to attack on the first turn they could phase in then end their turn outside the room and wait until their next turn to enter.

A solution I have used before with goblins is to have the goblins pour of out of holes in the walls (goblins are small so they can squeeze through 2.5' holes). The encounter ends when the party manage to plug the holes. You could do something similar with cursed urns that need to be destroyed or piles of evil bones that need to be incinerated to end the tide of ghosts.

  • \$\begingroup\$ "two on each side" should be "four on each side" since there are four 5' sections in a 20' length of wall (which, including corners, would give a total of 20 sections of 5' x 5' wall). \$\endgroup\$
    – MT0
    Mar 30, 2022 at 8:29
  • \$\begingroup\$ @MT0 Oh yeah you're right, 20'x20', cheers \$\endgroup\$
    – user73918
    Mar 30, 2022 at 8:54

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