How to Adjudicate Mental Prison

[Emongnome777]

Mental Prison is a 6th level spell from XGtE. Concentration, up to 1 minute, Int save. Here's a portion of the spell text:


On a successful save, the target takes 5d10 psychic damage, and the spell ends. On a failed save, the target takes 5d10 psychic damage, and you make the area immediately around the target’s space appear dangerous to it in some way. You might cause the target to perceive itself as being surrounded by fire, floating razors, or hideous maws filled with dripping teeth. Whatever form the illusion takes, the target can’t see or hear anything beyond it and is restrained for the spell’s duration. If the target is moved out of the illusion, makes a melee attack through it, or reaches any part of its body through it, the target takes 10d10 psychic damage, and the spell ends.

This gives a great deal of control in the DMs hands. A DM could rule that the creature just stands there cowering, giving a party free reign to beat it to death and it fail to respond for the duration of the spell. On the other end of the spectrum, a DM could say it uses its object interaction to reach through it, ending the spell and giving the creature its full compliment of actions for its turn.

My wizard is turning 12th level and I want to take this spell. I would prefer to work with my DM and create a "standard" response and was wondering what some people's opinions were. For a 6th level slot, if the creature never breaks through the spell, that seems too powerful. I'm thinking it makes an attack on its first turn, ending the spell, but also eating its action for a turn. Could there be different responses based on the creature's intelligence, for instance?

For me as either a DM or player, I'd prefer there be consistency in how the creature's response is adjudicated from one casting to another. It may be kinda boring doing that, but it avoids hurt feelings if the DM just takes the "easy way out" (object interaction as described above). Or maybe I'm making a mountain out of a mole hill.

[Unoriginal]

Mental Prison is a 6th level spell from XGtE. Concentration, up to 1 minute, Int save. Here's a portion of the spell text:



This gives a great deal of control in the DMs hands. A DM could rule that the creature just stands there cowering, giving a party free reign to beat it to death and it fail to respond for the duration of the spell. On the other end of the spectrum, a DM could say it uses its object interaction to reach through it, ending the spell and giving the creature its full compliment of actions for its turn.

My wizard is turning 12th level and I want to take this spell. I would prefer to work with my DM and create a "standard" response and was wondering what some people's opinions were. For a 6th level slot, if the creature never breaks through the spell, that seems too powerful. I'm thinking it makes an attack on its first turn, ending the spell, but also eating its action for a turn. Could there be different responses based on the creature's intelligence, for instance?

For me as either a DM or player, I'd prefer there be consistency in how the creature's response is adjudicated from one casting to another. It may be kinda boring doing that, but it avoids hurt feelings if the DM just takes the "easy way out" (object interaction as described above). Or maybe I'm making a mountain out of a mole hill.

IMO the fact there is no standard response because the response depends on the NPC you're casting it on is a feature, not a drawback. Using mind magic or illusions requiring the caster to think "how will this one react to that?" is good, and you can't treat a cowardly manticore the same way you can treat a berserking demon or a duty-bound-to-protect-their-charge guardian.

Also keep in mind that if they do break the illusion they still get 10d10 damages, so it's not like the spell is wasted either way.

[Rukelnikov]

Mental Prison is a 6th level spell from XGtE. Concentration, up to 1 minute, Int save. Here's a portion of the spell text:

This gives a great deal of control in the DMs hands. A DM could rule that the creature just stands there cowering, giving a party free reign to beat it to death and it fail to respond for the duration of the spell. On the other end of the spectrum, a DM could say it uses its object interaction to reach through it, ending the spell and giving the creature its full compliment of actions for its turn.

My wizard is turning 12th level and I want to take this spell. I would prefer to work with my DM and create a "standard" response and was wondering what some people's opinions were. For a 6th level slot, if the creature never breaks through the spell, that seems too powerful. I'm thinking it makes an attack on its first turn, ending the spell, but also eating its action for a turn. Could there be different responses based on the creature's intelligence, for instance?

Yeah, and not just intelligence, but personality/character, emotional state, previous experience.


For me as either a DM or player, I'd prefer there be consistency in how the creature's response is adjudicated from one casting to another. It may be kinda boring doing that, but it avoids hurt feelings if the DM just takes the "easy way out" (object interaction as described above). Or maybe I'm making a mountain out of a mole hill.

The thing is, creatures are creatures, not bots. Do you imagine a mind flayer, a dog, a wizard, and a raging barbarian reacting the same way to an illusion of being surrounded by terrifying creatures?

The dog may cower and probably stay put for the duration.
The flayer may attempt to intimidate them, probe their minds or blast them, and then if it realizes its an illusion try to break it or just ignore it and try to probe for minds beyond it.
The wizard may immediately Teleport away.
The barbarian may very well cross it like nothing on its turn taking the damage and recklessly attacking the closest foe.

Maybe you could make a similar spell, that instead of allowing the creature to react as normal, compels it to act in a certain way, that maybe should be an enchantment spell instead of an illusion though.

[Kvess]

I would prefer to work with my DM and create a "standard" response and was wondering what some people's opinions were. For a 6th level slot, if the creature never breaks through the spell, that seems too powerful.
Is it? Banishment is a 4th level spell and also targets an uncommon save. The only different is Mental Prison allows your allies to attack the ‘banished’ creature, and the creature can choose to take damage to free itself.

I would suggest having weaker-willed creatures cower until attacked, brave but low-intelligence creatures charge through, and intelligent creatures (who already have good saves against the spell) acting strategically. If a spellcaster is trapped, they could attempt to cast Dispel Magic, if it is prepared.

[Kvess]

The dog may cower and probably stay put for the duration.
The flayer may attempt to intimidate them, probe their minds or blast them, and then if it realizes its an illusion try to break it or just ignore it and try to probe for minds beyond it.
The wizard may immediately Teleport away.
The barbarian may very well cross it like nothing on its turn taking the damage and recklessly attacking the closest foe.
Jeremy Crawford (https://twitter.com/jeremyecrawford/status/1088511458927767553?s=21) has said that teleporting away would count as being moved out of the illusion, and would result in taking psychic damage.

[Abracadangit]

IMO the fact there is no standard response because the response depends on the NPC you're casting it on is a feature, not a drawback. Using mind magic or illusions requiring the caster to think "how will this one react to that?" is good, and you can't treat a cowardly manticore the same way you can treat a berserking demon or a duty-bound-to-protect-their-charge guardian.

Also keep in mind that if they do break the illusion they still get 10d10 damages, so it's not like the spell is wasted either way.

I agree with everything said here. I would add that the spell also lets you fluff the illusion however you want with each casting, which would also have an effect on how likely the monster is to try anything. Like plant creatures might not be all that put off by the hideous maws because body horror doesn't really register with them, but walls of fire will trigger their intense fear of flame. A little creativity goes a long way with this spell.

[Rukelnikov]

Jeremy Crawford (https://twitter.com/jeremyecrawford/status/1088511458927767553?s=21) has said that teleporting away would count as being moved out of the illusion, and would result in taking psychic damage.

I'm ok with that ruling.

[NorthernPhoenix]

I agree with the idea that it should be based on personality, but i also take a pretty dim view on just letting yourself be attacked for any reason. If you trap a creature and stop attacking them, the likelihood of them risking the real-to-them trap is quite small. They may even attempt to bargain or compromise if they are capable. If however, you keep attacking them, they get put in a "what have i got to lose" situation, and must break free, since their only choice is potentially die or certainly die.

[Hytheter]

15d10 damage is pretty nice single target damage even if it doesn't hold them for a second. It actually beats out Disintegrate for the same slot.

[EggKookoo]

On the other end of the spectrum, a DM could say it uses its object interaction to reach through it, ending the spell and giving the creature its full compliment of actions for its turn.

I don't think this is exactly right. The target will believe the illusion is real unless it 1) has reason to suspect it's not, and 2) makes a check (typically Int/Investigation) to confirm it. That check is normally considered its action for the turn, and still may fail, requiring it to try again (assuming the DM allows repeated checks) next turn. But still don't forget (1) -- the target doesn't know it's an illusion unless something tips it off.

I know this doesn't solve for the other end of the spectrum but I don't think its as broad as you suggest.

[Kvess]

There isn’t a general rule in 5e which states that interacting with illusions reveals them to be false. The description of spells like Silent Image specifically call out that physical interaction reveals them to be false and that a creature can make an Investigation check to reveal the illusion for what it is.

Other illusion spells like Mental Prison and Invisibility lack such rules for interaction. I would rule for attempts to interact with the illusory hazards in Mental Prison: short of attempting to pass a hand through would reveal nothing; passing a hand through would trigger the damage.

[EggKookoo]

Other illusion spells like Mental Prison and Invisibility lack such rules for interaction.

I feel like it's inherent in the concept of an illusion that the subject believes it's real unless given some reason to think otherwise. What's the purpose of the illusory component of mental prison if the subject knows it's fake?

[Kvess]

Just because you know you’re in a nightmare doesn’t mean you get to wake up. Otherwise knowing that a spellcaster specializes in illusion magic would mean that they’re essentially powerless.

[JackPhoenix]

Just because you know you’re in a nightmare doesn’t mean you get to wake up. Otherwise knowing that a spellcaster specializes in illusion magic would mean that they’re essentially powerless.

At least until the spellcaster remembers that being illusion specialist doesn't stop him from casting Fireball. Mixing in some real effects is the most effective way to use illusions anyway.

[Chronos]

Almost no enemies will say "I'm going to reach an arm through the illusionary hazards, because that will end the Mental Prison spell", because they don't know that's what it is. But they might say things like "OK, if I'm surrounded by toothy maws, then I'll attack one of the maws". Or "I'll carefully try to bend the thorny vines out of the way, to make an opening". Or "I'll try to jam something in the swirling blades". Or even just "I'll flail about madly in impotent rage". Any of those would trigger the damage and end the spell, not because of the nonexistant general rule about interacting with illusions, but because of the specific rule in this spell that if you reach or attack through it, it does damage and then ends.

And so you want to know enough about your enemy to know how they'll react, and choose a sort of hazard that they're less likely to try to reach through. It'd help if the player describes their reasoning when telling the DM what spell they're casting.

[MarkVIIIMarc]

Almost no enemies will say "I'm going to reach an arm through the illusionary hazards, because that will end the Mental Prison spell", because they don't know that's what it is. But they might say things like "OK, if I'm surrounded by toothy maws, then I'll attack one of the maws". Or "I'll carefully try to bend the thorny vines out of the way, to make an opening". Or "I'll try to jam something in the swirling blades". Or even just "I'll flail about madly in impotent rage". Any of those would trigger the damage and end the spell, not because of the nonexistant general rule about interacting with illusions, but because of the specific rule in this spell that if you reach or attack through it, it does damage and then ends.

And so you want to know enough about your enemy to know how they'll react, and choose a sort of hazard that they're less likely to try to reach through. It'd help if the player describes their reasoning when telling the DM what spell they're casting.

Is it generally conaidered that attacking the razors flying about you is "attacking through it"?

Or is attacking the illusion "attacking it"

My first thought of attacking through it was a trapped archer shooting an arrow blindly towards where she remembered the mage being. Maybe I am wrong.

[Segev]

The trouble is that I have seen PCs who will simply walk through a wall of fire to get to the other side, tanking the damage. Why wouldn't monsters do the same thing when faced with a mental prison that looks like a similarly passable hazard?

Now, we come to the question of how creatures respond to seemingly-impassible obstacles and prisons: what does a PC do when trapped in an iron cage with red-hot bars and razor-sharp, rusty barbs? Does he bash against it, and, if so, does he fail to break through because he's subconsciously rationalizing that it's too tough and he can't? Or does he automatically escape after taking one instance of damage? Or is it unreasonable to assume creatures - PCs included - would bash against so obviously painful a barrier, and thus wouldn't try it?

It's a lot easier, as usual, for a DM to run this against PCs: he describes the effect as they perceive it, and unless the PCs know the DM is likely to be using illusions, "it's an illusion" is not as likely to come to mind. (If it does, and the DM wasn't making an illusion, the PCs will suffer for testing it.)

When a PC uses it, though, the DM knows it's an illusion. So he can't benefit from the monster's true perspective and know for sure how the monster would act if it were definitely not an illusion, because he can't remove his own knowledge that it is.

[Kvess]

The monster eating a total of 15d10 psychic damage is not something that I, as a player, would consider to be a bad outcome from a 6th level spell. That's an average of 82.5 points of damage, and is a little better than Disintegrate (75 points of damage) cast at the same level.

I would feel the same if my spell made the monster sit on its hands during the rest of the fight, while remaining a target for attacks. Either effect is really good.

[EggKookoo]

When a PC uses it, though, the DM knows it's an illusion. So he can't benefit from the monster's true perspective and know for sure how the monster would act if it were definitely not an illusion, because he can't remove his own knowledge that it is.

Thus the purpose of needing to have a reason to suspect it's an illusion and the subsequent check. I mean we've all been down this "how do illusions work?" path before many times. FWIW as a DM I assume all illusions are inherently convincing until something tips off the observer.

[Segev]

Thus the purpose of needing to have a reason to suspect it's an illusion and the subsequent check. I mean we've all been down this "how do illusions work?" path before many times. FWIW as a DM I assume all illusions are inherently convincing until something tips off the observer.

Agreed, but my point is more this:

If you didn't, before the illusion came up, ever decide how a - say - ogre would react to being suddenly trapped in the eye of a sharknado, do you decide now, knowing the sharknado to be an illusion, that the ogre will refrain from getting hurt, will attack the sharks, or will dive through the wall of the sharknado to try to get at the caster who created it? Now, when you know it's an illusion, and thus exactly how effective it would be at stopping the dive-through maneuver?

It's a question of ability to separate your knowledge it's an illusion from how you have monsters act. Not when it's obvious that your choice is an excuse to ignore it, but when it is not obvious how something necessarily would react if the thing were really there.

[EggKookoo]

If you didn't, before the illusion came up, ever decide how a - say - ogre would react to being suddenly trapped in the eye of a sharknado, do you decide now, knowing the sharknado to be an illusion, that the ogre will refrain from getting hurt, will attack the sharks, or will dive through the wall of the sharknado to try to get at the caster who created it? Now, when you know it's an illusion, and thus exactly how effective it would be at stopping the dive-through maneuver?

My approach would be to first ask what the ogre would do if it thought the sharknado was real, independent of my knowledge. Would it try to punch its way through a bunch of real, actual sharks?

[NorthernPhoenix]

My approach would be to first ask what the ogre would do if it thought the sharknado was real, independent of my knowledge. Would it try to punch its way through a bunch of real, actual sharks?

Personally, I'd say yes, for ogres, but maybe not for a different type of foe.

[Segev]

My approach would be to first ask what the ogre would do if it thought the sharknado was real, independent of my knowledge. Would it try to punch its way through a bunch of real, actual sharks?

That is the ideal, yes. My point is that answering that and being sure you're not Being influenced in your answer by knowing that items an illusion is hard. It is something I don't trust myself with as a DM, even though I do my best.

[Kvess]

Do what indecisive DMs always do: Find out if the player wants the creature to try to break out or stay put, ask them if they prefer even or odds, and roll a die.

[Chronos]

In this case, just running through the hazard certainly isn't an option, because one of the effects of the spell is to restrain the target. You have to get rid of the obstruction before you can run through it.

[EggKookoo]

Do what indecisive DMs always do: Find out if the player wants the creature to try to break out or stay put, ask them if they prefer even or odds, and roll a die.

I don't see illusions as any different from any other process of dealing with metagame knowledge. The DM has all kinds of information about the state of the game that the monsters don't. It's part of being a DM to separate these things, as it's part of being a regular player. The DM just has more of it to deal with at any particular time.

There's nothing special about illusions with regard to this. If the DM is like me and views all illusions as convincing unless something indicates otherwise, the monster thinks the illusion is real, and the DM runs the monster accordingly. If the DM sees only some illusions as automatically convincing based on the specific description of the spell that created it, the monster sees the illusion as real for those spells that say so, or "just an illusion" for those that don't, and again is run accordingly.

It comes down to how the DM views illusions in the game.