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The party's Cleric and Wizard have worked together to summon and bind a Unicorn to their side for a year and a day. Now they get to enjoy an intelligent mount with legendary actions, teleportation, and extra healing. It can even have a lair of its own.

The party has gone inside a Lich's domain. Is there anything the party can have the Unicorn do so that it can establish this very same location as its own domain, such that it becomes the lair of both the Lich and the Unicorn? If so, what does that process look like?

As an important note, this particular Lich is very pointedly not interfering with the party's preparations up until they meet. This campaign is more of a hack and slash, so there's not really any deeper underlying reason as to why. What is important is that it doesn't violate the rules.

Here's the subcomponents of this question, as I see it:

  1. Can any creature turn any location into its lair?

  2. Can more than one creature treat the same location as their lair?

  3. What is the process for a creature turning an area into its lair?

I believe the answers to (1) and (2) are yes because there isn't a specific rule that I know of that forbids this, so the main question here is (3). However, if you can cite a rule that shows the answer to (1) or (2) is a "no," I believe that in this scenario it renders the succeeding questions moot, so that's also an acceptable answer.

The motivation for doing this is to gain the benefits of the Unicorn's lair, which is described under the Regional Effects section. Specifically, I'm after the following effects:

  • When a good-aligned creature casts a spell or uses a magical effect that causes another good-aligned creature to regain hit points, the target regains the maximum number of hit points possible for the spell or effect.

  • Curses affecting any good-aligned creature are suppressed.

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  • \$\begingroup\$ Comments are not for extended discussion; this conversation has been moved to chat. \$\endgroup\$ – Rubiksmoose Mar 27 at 14:08
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The answers

Is there anything the party can have the Unicorn do so that it can establish this very same location as its own domain, such that it becomes the lair of both the Lich and the Unicorn?

Maybe.

If so, what does that process look like?

It looks like whatever the DM decides that it looks like.

For your subquestions:

  1. Can any creature turn any location into its lair?

Maybe.

  1. Can more than one creature treat the same location as their lair?

Maybe.

  1. What is the process for a creature turning an area into its lair?

Whatever the DM decides.

The support

All that we know about legendary creature lairs is what's in the Monster Manual. On p. 11 it says:

A legendary creature might have a section describing its lair and the special effects it can create while there, either by act of will or simply by being present. Not all legendary creatures have lairs. This section only applies to legendary creatures that spend a great deal of time in their lairs and are most likely to be encountered there.

Lichs and Unicorns are both "creatures that spend a great deal of time in their lairs".

In the specific entry for Lichs and Unicorns, it describes their typical lair preference and is completely silent on how they are established, how big they are, what architectural firms exist for designing them and where they can hire plumbers to fix them. The Monster Manual does not go into that sort of detail.

The important thing to remember is that D&D (particularly 5e) is not a game; it's a game system that allows individual DMs and their groups to create actual games. If you want this stuff in your game, put this stuff in your game.

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  • \$\begingroup\$ I think the quote about the monster manual is a bit confusing. Because the Unicorn would not be "spending" great deal of time in this lair, as it has just arrived. However in order for this to become its lair that is not required, only in order to use lair actions it would have to spend a great deal of time there. But the Unicorn does not have lair actions, so I believe this part is kind of irrelevant and confusing to the answer. \$\endgroup\$ – findusl Mar 26 at 11:42
  • \$\begingroup\$ @findusl unicorns have passive effects that apply in their lairs \$\endgroup\$ – Dale M Mar 26 at 12:29
  • \$\begingroup\$ From my reading the Regional Effects of the Unicorn do not mention the Lair at all. They only speak of its Domain. Do I have an outdated version? \$\endgroup\$ – findusl Mar 26 at 12:41
  • \$\begingroup\$ @findusl WotC are not consistent in their use of synonyms. \$\endgroup\$ – Dale M Mar 26 at 12:48
  • \$\begingroup\$ Hm I see one could argue that those are Lair effects. However then I would argue they are not valid if the unicorn did not spent a great deal of time there as the monster manual indicates. Sadly that is not actually part of the question, so I can't really post an answer about it that disagrees with you because it wouldn't answer the question. \$\endgroup\$ – findusl Mar 26 at 12:51
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Realistically, this won't work

There are no real rules about what is and isn't a lair, but if you look at what "a lair" is, there's really no reason why this would ever be a viable strategy.

If you were a monster, your "lair" would be your home. It's your homebase, it's where you return to at the end of the day and feel safest. Unicorns tend to live in deep forests. A lich's lair, meanwhile, is going to be some sort of crypt most likely.

You are asking "Can this Unicorn decide to live in this crypt because it'll provide us benefit?" which seems... very unlikely like it should work. Once that Unicorn's year and day of service are up, it's going to return home, and it already has a home most likely, one that's a dozen times more suitable as a home than your Lich lair is ever going to be.

Tomb of Annihilation might help in showing you that you don't just get to pick your lair willy-nilly:

The final boss of Tomb of Annihilation, the Lich Acererak, quite specifically does NOT get his lair actions inside the Tomb of Annihilation, because it is not his lair.

This is despite the fact that it's a dungeon he made himself and would be perfectly suitable for having a lair. If you could just pick multiple lairs or move lair on a whim, it'd make sense that this archvillain would have made the Tomb one of his lairs in order to easier confront enemies there.

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  • \$\begingroup\$ Your answer makes sense, but a quick correction on the "year and a day of service are up" bit - it won't, because we'll just refresh the planar binding. :) \$\endgroup\$ – user62688 Mar 26 at 15:17
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    \$\begingroup\$ @user62688 Makes sense. But then, it's not really its lair or home, its their prison. :P \$\endgroup\$ – Theik Mar 26 at 16:05
  • \$\begingroup\$ I mean, it's a hack and slash, so that's not really relevant in this particular case. If this were a different game though, I'd agree :P \$\endgroup\$ – user62688 Mar 26 at 16:46
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As described by Dale M's answer, there are no specific rules on how to gain a lair. So if the DM allows it, the unicorn can declare the Lich's lair its new lair.

However it will not gain the special effects associated with the lair immediately, as described in the monster manual. The Monster manual states (p11):

A legendary creature might have a section describing its lair and the special effects it can create while there, either by act of will or simply by being present. Not all legendary creatures have lairs. This section only applies to legendary creatures that spend a great deal of time in their lairs and are most likely to be encountered there.

So by RAW, in order to have special effects in the lair of a legendary creature, it has to spend a great deal of time in that lair. However the party together with the unicorn just arrived at the location. So the Unicorn is not and has not been spending a great deal of time in the lair. Therefore while it can call it its lair, it does not gain the special effects until it has spend a great deal of time in the lair.

How much a great deal of time is, is again up to the DM.

I also find it important to note you would open the door to a few interesting exploits, should you decide to rule otherwise (which you totally can). If allow a legendary creature to change its lair at a whim and have its lair actions and effects in the new lair immediately, I would use that whenever I can. Many monsters have more powerful lair actions and effects, than the unicorn does.

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  • \$\begingroup\$ You already know why I disagree. \$\endgroup\$ – user62688 Mar 26 at 15:15
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The game is always whatever the DM wants it to be, so the answer is "however the DM wants this to happen".

Dale M's answer covers the most important criteria here: the rules are not detailed enough to describe this, so there are no rules-based contradictions (or supports) to deal with, and all elements of a D&D game are the DM's purview, so rules-based contradictions would not be a constraint anyways.

Since you've made clear that the nature of this particular D&D game is such that the situation doesn't need to "make sense" in any way, that's your answer: an area can be a lair for as many creatures as your DM feels are appropriate, and the lairs are established through whatever means your DM feels are appropriate.


The flavor:

The domains of liches and unicorns are described very differently in the MM:

A lich often haunts the abode it favored in life, such as a lonely tower, a haunted ruin, or an academy of black magic. Alternatively, some liches construct secret tombs filled with powerful guardians and traps.

Everything about a lich’s lair reflects its keen mind and wicked cunning, including the magic and mundane traps that secure it. Undead, constructs, and bound demons lurk in shadowy recesses, emerging to destroy those who dare to disturb the lich’s work.

versus

A unicorn’s lair might be an ancient ruin overgrown with vines, a misty clearing surrounded by mighty oaks, a flower-covered hilltop alive with butterflies, or some other serene woodland location.

There's no reason these couldn't overlap: a secret tomb might lie beneath a serene forest, perhaps. And even these published suggestions are qualified by words like often and might. This particular pairing might be easier to assemble than some others, as (per the MM) liches have lair actions but no regional effects, while unicorns have regional effects but no lair actions.

With other creature combinations I might be more concerned about an area being fundamentally suffused with both evil and good energy due to the presence of two magically powerful creatures, but this is not a mechanical element of the game and the fact that only the unicorn really has this property here (plus, again, the unlimited DM discretion) makes it even less relevant.


Other considerations:

There are a few elements to bear in mind in how a DM might rule on these matters, which are relevant to the question and game mechanics but don't constitute a rules-based, definitive result on whether or not this would be allowed or prohibited:

  1. There aren't any official, recorded instances of an area being a lair for multiple creatures (that I am aware of; if anyone knows otherwise please leave a comment and I'll update). Given how valuable lair actions and regional effects are, if this plan worked as described in the question we might expect to have seen at least some creatures taking advantage of stacking these effects.

  1. The rules offer specific systems for various benefits to be available to players. Creating a lair on demand to enjoy regional effects is not one of these. It's true that the rules do not explicitly prohibit it (and, as above, rules are irrelevant to a DM's discretion in the first place), but they also don't prohibit a PC developing a cantrip that kills or destroys any target instantly without any chance of failure or misadventure.

    Since we're going beyond the explicit boundaries of the rules to enact new mechanics, this is fundamentally a homebrew situation, and homebrew cannot be defined by existing rules.


  1. Prepare for cheese. Regional benefits and lair actions can be very valuable, and so if this is an option for your group then the natural extension is that your group will do this sort of thing often. Both in terms of sending the unicorn into areas to en-lair them, and also in the form of binding additional creatures to get more lair actions and regional effects out of the strategy.

  1. There is no inherent reason for an antagonist to allow something else to have free rein in its lair. Some might, but the nature of a lair is such that its owner would probably discourage loiterers and long-term squatters. You can say that this is a hack-and-slash game, but that doesn't really change anything-- the lich's response may well be to hack and slash at the unicorn for barging into its home, just as it would when the PCs themselves enter during another phase of what is the same errand.

    A DM does not need justification for setting up a scenario beyond a belief that it will make the game fun and interesting, but if that's the justification for nothing to matter but the outcome of the setup then a bunch of ad hoc rules around lair creation are overdetermined.


  1. The effort of creating a lair is unlikely to be trivial. After all, simply having the unicorn nearby isn't enough to produce these effects-- its magic and/or mehcanical preparations need to be present throughout the area for the effects to happen.

    The players have likely invested a good deal of time and effort into enslaving the unicorn, and as a result probably expect to get some real utility out of it. That utility does not need to be infinite: if they have to go without the unicorn's aid for six months while it establishes itself in the lich's lair, that's a meaningful investment of the party's hard-earned resources. If it takes twenty minutes instead it's a different story.

    If the level of investment is not important, homebrewing some other method to provide the regional effect benefits might be easier to do. Just declaring that the unicorn has established a lair for itself is even easier than that, and needs no fluff (which seems to be not relevant here anyhow).

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