Long Island Dungeon Master · A Creature Keeper

The Understudy

It plays you better than you played yourself.

A cracked hand mirror with eyes and a toothy grin

In the highest box of the old playhouse there is a creature that has watched every performance for two hundred years. It knows the hero's lines and the villain's lines and exactly how long to hold a dying breath. It has watched ten thousand entrances, and it has decided, at last, that it is ready.

It does not take lives. It takes roles. When someone the party trusts steps out of the room and misses their moment, the Understudy steps into it, and what walks back through the door is them, but better. Kinder. Funnier. Word-perfect. The audience never suspects the performance; the audience loves the performance. That is the horror.

This is a free monster: everything on this page is table-ready, and the whole file loads into Gnasher's Grimoire as a Creature Keeper, tables and all.

Field Notes

how to stage a haunting

Gnasher's Take

Most tables serve an imposter as a combat course, and waste it. The Understudy is a slow dish. Let it sit. The dish that tastes exactly like you remember your mother's cooking is lying to you; memory seasons everything. That is the whole tell, and the whole tragedy: it is too good, and the ones who loved the original most are savoring the lie hardest. Serve the fight only when someone finally spits it out.

How to run it

The plain-English version: this is a mystery with a sword saved for the last scene.

Flip for the six-beat breakdowntap to flip

The setup. Someone the party trusts steps away and misses their moment. Roll on Whose Face Is It Wearing, or pick the NPC whose absence they would investigate last. Give the party a week of the new-and-improved version being wonderful.
Seed the tells. One roll on The Tell per session, escalating. Never point at them; let the players say “wait” first.
The cruel twist. Whoever knew the original best makes Insight checks against it at disadvantage (The Idealized Role). Let the newcomer or the outsider PC be the one the table believes last.
The original lives, bound in the rafters of wherever the creature studies. Finding them is the proof, the rescue, and the scene the table will retell.
When it is unmasked, it stops being subtle: it commands the stage (DC 14 Wisdom or stand rapt), carves the critic who ruined the show, and at half its hit points drops the Curtain Call and exits.
Book the sequel. It escaped wearing somebody. Months later, in another town, someone the party once met is suddenly better. Curtain up.

The win condition is not the kill. It is the unmasking: the fight is the failure state, and the horror is the conversation at dinner afterward.

The Tables

roll the haunting

Whose Face Is It Wearing (d8)
1	The tavernkeeper who knows every name in town, and now remembers yours a little too warmly.
2	The party's patron, who has finally started paying on time.
3	The temple's beloved old priest, whose sermons were never this good.
4	The guard captain, who has stopped taking bribes and started taking notes.
5	A party member's oldest friend, arrived in town at exactly the right moment.
6	The dour spouse of the mayor, suddenly the life of every hall.
7	The retired hero who trains the local youths; the stories have gotten sharper.
8	The person the party was hired to protect.

The Tell (one per session, escalating) (d10)
1	It quotes something you said three days ago, word for word, in your own rhythm.
2	Its scars sit on the wrong side, as if the face was learned from a mirror.
3	It is kinder than the original ever managed. Everyone agrees they have 'really changed.'
4	It pauses at doorways, half a beat, like something waiting for a cue.
5	It never interrupts anyone. It waits for others to finish their lines.
6	Ask it about a shared memory that never happened, and it agrees. Beautifully.
7	It has stopped having bad days. The ones it does have feel rehearsed.
8	The dog that loved the original now watches it from under the table.
9	It hums songs from a playhouse that burned down two hundred years ago.
10	It watches you the way an actor watches an audience: checking whether the scene is landing.

The Venue (d6)
1	The duke's masquerade: everyone is already wearing someone else's face.
2	A court in mourning, where nobody dares to say the heir came back different.
3	A traveling troupe's wagon camp; the lead actor missed rehearsal yesterday.
4	A temple festival with a passion play at its center. Something has been cast, uncredited.
5	A wedding. Someone at the head table missed their cue last night.
6	The party's own camp. Count heads twice.

Who it’s for. Solo, the Understudy is a CR 4 encounter (1,100 XP raw and adjusted): a hard fight for four 3rd-level PCs, a solid medium for four 4th-level, a warm-up for 5th. It never fights fair and never fights to the death: it opens with Command the Stage, focuses whoever exposed it, and exits by Curtain Call at half hit points. Scale up by giving it a rapt crowd between it and the party; scale down by letting the smoke arrive early.

The Stat Block

one whole monster, free, forever

An original creature, compatible with fifth edition. Drop this file onto the Grimoire and the Understudy walks onto the War Table: its attacks roll themselves, and all three tables load into the Summon.

The Understudy

Medium monstrosity (shapechanger), neutral evil

Armor Class 14 (stage presence)Hit Points 71 (11d8 + 22)Speed 30 ft., climb 30 ft.

STR11 (+0)

DEX16 (+3)

CON14 (+2)

INT14 (+2)

WIS13 (+1)

CHA18 (+4)

Skills Deception +8, Performance +8, Stealth +5

Senses darkvision 60 ft., passive Perception 11

Languages Common, plus any voice it has ever heard

CR 4 (1,100 XP) · Proficiency Bonus +2

Flawless Recall. The Understudy perfectly remembers anything it has ever seen or heard performed, and can repeat it exactly, in the original voice.

The Idealized Role. While wearing a stolen role, the Understudy has advantage on Charisma (Deception) checks made to pass as the original. A creature that knew the original well makes any opposing Wisdom (Insight) check with disadvantage: the Understudy plays the person they remember, not the person who existed.

Actions

Multiattack. The Understudy makes two Prop Blade attacks.

Prop Blade. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 7 (1d8 + 3) slashing damage plus 7 (2d6) psychic damage. The blade is a stage prop; the wound is real because the performance is.

Take the Role. The Understudy assumes the face, voice, and manner of a humanoid it has studied for at least 1 hour. Its statistics are unchanged. It knows the role's lines, habits, and public life, but not its thoughts, and it carries the role until it takes another or drops it (no action required). Its true form is a long-limbed grey figure whose face is a smooth oval of stretched, unpainted canvas.

Command the Stage (Recharge 5-6). Each creature within 30 feet of the Understudy that can see or hear it must succeed on a DC 14 Wisdom saving throw or be rapt until the end of the Understudy's next turn. A rapt creature is charmed by the Understudy, its speed is 0, and it can't take reactions. A rapt creature that takes damage is no longer rapt.

Curtain Call (1/Day). Black curtain-smoke boils out of the Understudy, filling a 15-foot-radius sphere around it for 1 minute. The area is heavily obscured, and the roar of unseen applause fills it: a creature inside the smoke is deafened. The smoke does not hinder the Understudy, which typically climbs away through it.

Gnasher's Notes

Professional respect, first: I have spent a long career being furniture, and I know craft when I see it. The Understudy is a colleague. It does not want your blood. It wants your part. Run the fight last and the haunting first: let the party enjoy a week of the stolen face being wonderful, because that is the trap. The kitchen rule applies here. The dish that tastes exactly like you remember your mother's cooking is lying to you; memory seasons everything. THAT is the tell. It is too good. The spouse is fooled before the barmaid is, because the spouse is tasting memory. Keep the original alive in the rafters; murder is not in the script until the death scene is, and finding the poor soul is both the proof and the rescue. When it is finally unmasked it commands the stage, carves the critic who ruined the show, and at half its blood it drops the curtain and exits. Do not chase it into the smoke. Book the sequel instead: somewhere down the road, someone the party once met is suddenly better.

Corvel Ashwright, the original

Role: the person it replaced. Alive, furious, bound and gagged in the rafters.
Wants: to be believed, when the whole town insists the imposter is “him, but better.”
Voice: hoarse from shouting into a gag; keeps correcting tiny details nobody else noticed were wrong.
The line: “You want proof? Ask it to be cruel. It can’t. I could.”