Mental Prison, if the target moves out of the area.....

[MarkVIIIMarc]

This one has me assuming a couple things. Maybe I need to just ask for examples of how it works but here is my guess:

Lets say an NPC, Violet, casts Mental Prison on a Paladin, Jericho who fails the save. Jericho's team mates are just going to see him looking around like a mime cowering from an invisible maw chewing on him. How does a DM describe this?

The team mates will no doubt yell something to Jericho so unless its scary as heck, he'll try to leave the prison on his turn and take the 10D10 damage...

As a DM how do I describe this thing?

************************************
6th-level illusion
Casting Time: 1 action
Range: 60 feet
Components: S
Duration: Concentration, up to 1 minute
You attempt to bind a creature within an illusory cell that only it perceives. One creature you can see within range must make an Intelligence saving throw. The target succeeds automatically if it is immune to being charmed. 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.

[Man_Over_Game]

Lots of raving, lots of screaming.

No joke. That's how I'd do it. "NO! DON'T COME ANY CLOSER. NO DAMMIT. _NONONONOOOOOOOOO!"

In comparison, assuming a 50% miss chance, Chain Lightning does about 34 damage to 4 creatures. So...seems fair that MP is pretty debilitating.

[Segev]

What book is that from? Or is it homebrew?

[MaxWilson]

What book is that from? Or is it homebrew?

It's from Xanathar's.

[Millstone85]

The team mates will no doubt yell something to Jericho

Which he will not be able to hear.

[MaxWilson]

Which he will not be able to hear.

Cue endless debates about whether you automatically know the location of an enemy you cannot see or hear but who has not taken the Hide action. :-P

[MarkVIIIMarc]

Which he will not be able to hear.

See of hear! Got it. The PC has no idea it isn't real.

Me as DM, "Jericho, you see a swirling mass of bone daggers rising from the ground to completely envelope you. The mass is soo thick and moving soo quickly you can't see through them and they make such a swirling air rushing racket you can hear nothing else." Then, make an Intelligence Saving throw" and give damage appropriately.

On the next turn if he hasn't rushed or attacked them I'll have him make another Int save and so on. Id they stay I'll say they surround him perfectly.

[MaxWilson]

On the next turn if he hasn't rushed or attacked them I'll have him make another Int save and so on. Id they stay I'll say they surround him perfectly.

He's not supposed to get more than one save against this spell.

[Tiadoppler]

See of hear! Got it. The PC has no idea it isn't real.

Me as DM, "Jericho, you see a swirling mass of bone daggers rising from the ground to completely envelope you. The mass is soo thick and moving soo quickly you can't see through them and they make such a swirling air rushing racket you can hear nothing else." Then, make an Intelligence Saving throw" and give damage appropriately.

On the next turn if he hasn't rushed or attacked them I'll have him make another Int save and so on. Id they stay I'll say they surround him perfectly.

Keep in mind that the spell also Restrains him, so his speed is 0. He cannot move out of the area (edit: he can be moved by certain effects, but he can't just run out) until the spell ends.

Also, he only gets one save for that spell.

[Dalebert]

Keep in mind that the spell also Restrains him, so his speed is 0. He cannot move out of the area (edit: he can be moved by certain effects, but he can't just run out) until the spell ends.

Right, so someone could shove him out, for instance, and end it, but also cause the 10d10.

[Coffee_Dragon]

What book is that from? Or is it homebrew?

It's what people claim Phantasmal Force does.

[DMThac0]

To party: "You see Jericho standing still as a statue, there is a look on his face that is a combination of fear and pain. His eyes seem to be out of focus as though looking at something a few inches in front of him."

To Jericho: "Out of the ground, the air, all around you a hazy image starts to form. There is a shrill hum that pierces your ears, but it is more like it's in your head. Screams and cries, howls and snarling, all eminate from this image, the sound so overwhelming it drowns out the world. The image shifts, demons, terrifying monsters, nightmares, fears, all appearing and disappearing as you shift your gaze. "

---
Jericho cannot leave the area himself as he's restrained, but he can lash out which may cause him to penetrate the illusion causing the psychic damage.

His party can try to call out all they want, it'll have no effect, and if they try to move him he'll take the psychic damage.

[Dalebert]

His party can try to call out all they want, it'll have no effect, and if they try to move him he'll take the psychic damage.

Yes, but he'll be free. It's a lose-win situation. ;)

[1Pirate]

Not the best spell against Paladins though. One Oath is immune to it, another has resistance, and any 14+ can just Cleanse it.