When it came to the finale at my weekly library game, everyone showed up. And that's how I found myself managing nine players vs. a giant monster.
With that many players—a number that doubles the standard adventuring party—we moved from combat encounter to siege of dramas. The Avatar of Voynich, a plant-like fiend sprouting six pumpkin heads, was designed to do more than just swing a vine; it was engineered to dismantle the party's coordination, both physically and psychologically.
The PCs were trapped in a cabin. Our gnome assassin (Nixel) was down in the cellar after having just defeated the hag (who ended up being the vessel for the Avatar's arrival after her corpse was dragged out by a spirit of the Avatar into the woods), but was infected by her claws, losing a point of Charisma each around as vines sprouted from the wound. He was with the tiefling wizard's (Percipience) owl familiar (Fica), an important form of communication because there were clues in the cellar as to how to stop the Avatar.
Four of the PCs were in the cabin itself, a vulnerable, rickety old thing that provided both cover and potential roof collapse when the Avatar took hold (which it did). Three more attacked it from the woods from behind, with only trees to hide behind.
To counter this, the Avatar of Voynich required a significant overhaul in hit point elasticity and action economy. Traditionally, a CR 4 monster might possess 60 to 90 hit points, but against nine players, such a creature would survive exactly one round. To help my poor Avatar survive, he was going to need a few tricks.
The Avatar needed to be tough enough to survive, but not so lethal that it could wipe the party in a single turn. This balance was achieved through a combination of resistances and the implementation of a Legendary Action pool that scaled with the number of participants.
The obvious change was Legendary Resistance and Legendary Actions, both of which are designed to keep monsters from being easily overwhelmed. Ironically, at third level the party didn't cast a single "save-or-fail" spell, opting instead for damage inflicting options, so for all my worry about Legendary Resistance, it never came up.
Legendary Actions, on the other hand, were crucial. In the 2024 edition, monsters all seem to get a base three Legendary Actions, four in their lair (which the Avatar was). But instead of having the Avatar inflict just damage, it also could inflict the Stunned condition. This meant that it could keep some PCs out of the fight while others were trying to free their allies or help up downed foes.
The most useful aspect of the Avatar wasn't a Legendary Action at all, but the "Roper-style" vine drag. This serves a dual purpose: it physically displaces the character, often moving them out of range of their allies' buffs (like a Paladin’s aura or a Bard's inspiration), and it forces the party to spend their own movement and actions to save their allies. The Avatar's tendrils had less hit points and were easier targets; with a six-headed monster chomping on anyone in melee, fighting the Avatar hand-to-hand practically guaranteed someone would go down. When the Avatar wasn't dragging PCs out of the shelter of the cabin, it used its tendrils to tear the cabin's foundation apart, collapsing the roof on some of them.
A battle against a high-hit-point monster can easily devolve into a slog if there is no other objective. To combat this, I introduced three side dramas that functioned as simultaneous encounters, effectively splitting the nine players into smaller, more manageable sub-groups. This mimics the Evil Dead style of horror where the environment is as much an enemy as the monster itself.
The mechanic was simple yet terrifying: a Constitution saving throw at the start of each turn, with the DC increasing by 1 each round. Success meant the infection stayed at bay; failure resulted in a 1 point reduction in the Charisma score as tendrils extended from the wound. If Nixel's Charisma reached zero, he knew what would happen--the PC would become a plant zombie like the poor NPC ally, an extension of the Avatar’s will. Nixel, communicating with the party via the Perci's familiar, Fica, alternated between scrambling for clues and trying to burn off the vines while injuring himself in he process. Which is how he found out about...
This three-part structure ensured that all nine players had something vital to do. The martial characters focused on the Avatar, the rogue dealt with the possession and the basement, and the spellcasters identified the book as the true source of the monster's power. By the end of the session, the Avatar was down to 2 hit points, the book was at 5, and three PC were unconscious. When they finally killed it and destroyed the book, the hard-won success felt earned and fitting for the conclusion of a eight-month arc.
What that resulted in, however, was three different dramas: the frantic clue-searching in the cellar as Nixel tried to save himself and the party; Marxenne trying to stop her possessed hand from choking her to death; and the casters destroying the book tied to the Avatar to banish it for good. All the while, the tanks whacked away at the Avatar the old fashioned way, even as it dragged them through the forest, smashing them against trees and stunning them in-between taking big bites of those who got dragged too close
And yet despite the chaos, it worked. Of the PCs who were actually fighting the Avatar, only five were inflicting damage: one was in the cellar, one was buried, one was trying to destory the book, and one was fighting her own hand. And yet everyone felt like they were doing SOMETHING, and each PC was critical to the survival of the group as a whole.
The finale of this arc taught me something important about how epic boss battles should work: not just hit points and armor class and actions, but multiple environmental factors at once (searching for clues, collapsing cabins, burning books) that gives everyone a chance to risk it all while under immense pressure. Sometimes, heroics isn't just battling bags of hit points, but finding the right clue at the right time.
Your Turn: How do you run big group boss fights?
With that many players—a number that doubles the standard adventuring party—we moved from combat encounter to siege of dramas. The Avatar of Voynich, a plant-like fiend sprouting six pumpkin heads, was designed to do more than just swing a vine; it was engineered to dismantle the party's coordination, both physically and psychologically.
The PCs were trapped in a cabin. Our gnome assassin (Nixel) was down in the cellar after having just defeated the hag (who ended up being the vessel for the Avatar's arrival after her corpse was dragged out by a spirit of the Avatar into the woods), but was infected by her claws, losing a point of Charisma each around as vines sprouted from the wound. He was with the tiefling wizard's (Percipience) owl familiar (Fica), an important form of communication because there were clues in the cellar as to how to stop the Avatar.
Four of the PCs were in the cabin itself, a vulnerable, rickety old thing that provided both cover and potential roof collapse when the Avatar took hold (which it did). Three more attacked it from the woods from behind, with only trees to hide behind.
The Mathematics of the Mob
At 3rd level, a party of nine can output a staggering amount of damage in a single round. If each player manages a conservative average of 8 damage per hit, the boss faces 72 damage per round before account for critical hits, smites, or action surges.To counter this, the Avatar of Voynich required a significant overhaul in hit point elasticity and action economy. Traditionally, a CR 4 monster might possess 60 to 90 hit points, but against nine players, such a creature would survive exactly one round. To help my poor Avatar survive, he was going to need a few tricks.
The Avatar needed to be tough enough to survive, but not so lethal that it could wipe the party in a single turn. This balance was achieved through a combination of resistances and the implementation of a Legendary Action pool that scaled with the number of participants.
The obvious change was Legendary Resistance and Legendary Actions, both of which are designed to keep monsters from being easily overwhelmed. Ironically, at third level the party didn't cast a single "save-or-fail" spell, opting instead for damage inflicting options, so for all my worry about Legendary Resistance, it never came up.
Legendary Actions, on the other hand, were crucial. In the 2024 edition, monsters all seem to get a base three Legendary Actions, four in their lair (which the Avatar was). But instead of having the Avatar inflict just damage, it also could inflict the Stunned condition. This meant that it could keep some PCs out of the fight while others were trying to free their allies or help up downed foes.
The most useful aspect of the Avatar wasn't a Legendary Action at all, but the "Roper-style" vine drag. This serves a dual purpose: it physically displaces the character, often moving them out of range of their allies' buffs (like a Paladin’s aura or a Bard's inspiration), and it forces the party to spend their own movement and actions to save their allies. The Avatar's tendrils had less hit points and were easier targets; with a six-headed monster chomping on anyone in melee, fighting the Avatar hand-to-hand practically guaranteed someone would go down. When the Avatar wasn't dragging PCs out of the shelter of the cabin, it used its tendrils to tear the cabin's foundation apart, collapsing the roof on some of them.
A battle against a high-hit-point monster can easily devolve into a slog if there is no other objective. To combat this, I introduced three side dramas that functioned as simultaneous encounters, effectively splitting the nine players into smaller, more manageable sub-groups. This mimics the Evil Dead style of horror where the environment is as much an enemy as the monster itself.
Drama I: The Possession
The first complication involved an NPC ally, who ended up getting infected by the hag and turned into a plant zombie (a warning for Nixel and Marxenne, our dragonborn war cleric). In that same battle, Marxenne discovered the wound on her arm had rapidly become infected. Her hand started strangling her own throat. This created an immediate moral and tactical dilemma. It required at least two PCs to grapple the NPC and attempt checks to break the possession. The DC to resist the claw increased by 1 each round. It also removed two actions from the party's pool every round as PCs split their focus between fighting the Avatar and helping Marxenne, reducing their total offensive output by over 20%. By forcing players to choose between damaging the boss or saving the PC from themselves, the encounter shifted from a math problem to a heroic narrative.Drama II: The Cellar Infection
While the main fight raged in the cabin's common room, Nixel was trapped in the cellar, facing a creeping fungal infection that sapped his Charisma every round.The mechanic was simple yet terrifying: a Constitution saving throw at the start of each turn, with the DC increasing by 1 each round. Success meant the infection stayed at bay; failure resulted in a 1 point reduction in the Charisma score as tendrils extended from the wound. If Nixel's Charisma reached zero, he knew what would happen--the PC would become a plant zombie like the poor NPC ally, an extension of the Avatar’s will. Nixel, communicating with the party via the Perci's familiar, Fica, alternated between scrambling for clues and trying to burn off the vines while injuring himself in he process. Which is how he found out about...
Drama III: The Bonded Book of Voynich
The most significant twist was the discovery of a sentient, plant-like book bonded to the Avatar. This book shared a life-link with the monster. The book had its own hit points (matching the Avatar's) and AC, but it was vulnerable to fire and slashing damage—the traditional weaknesses of plant monsters. The PCs alternated between trying to kill the terrifying Avatar from a distance and using melee attacks against the book itself, a vulnerability communicated to the PCs upstairs by Nixel downstairs.This three-part structure ensured that all nine players had something vital to do. The martial characters focused on the Avatar, the rogue dealt with the possession and the basement, and the spellcasters identified the book as the true source of the monster's power. By the end of the session, the Avatar was down to 2 hit points, the book was at 5, and three PC were unconscious. When they finally killed it and destroyed the book, the hard-won success felt earned and fitting for the conclusion of a eight-month arc.
The "Rule of Three" Dramas
Candidly, I didn't plan this. I ran multiple battle simulations trying to figure out how the heck the Avatar was going to survive nine PCs, with the real possibility they might not all show up. I also didn't intentionally separate the PCs -- the two rogues were down in the cellar, but one was terrified by the hag and fled, leaving Nixel and Fica separated from the party when the Avatar collapsed the cabin's roof. Three PCs joined late, so they came at the monster from behind, attacking it at a distance (well, not quite, three PCs just charged it from different directions).What that resulted in, however, was three different dramas: the frantic clue-searching in the cellar as Nixel tried to save himself and the party; Marxenne trying to stop her possessed hand from choking her to death; and the casters destroying the book tied to the Avatar to banish it for good. All the while, the tanks whacked away at the Avatar the old fashioned way, even as it dragged them through the forest, smashing them against trees and stunning them in-between taking big bites of those who got dragged too close
And yet despite the chaos, it worked. Of the PCs who were actually fighting the Avatar, only five were inflicting damage: one was in the cellar, one was buried, one was trying to destory the book, and one was fighting her own hand. And yet everyone felt like they were doing SOMETHING, and each PC was critical to the survival of the group as a whole.
The finale of this arc taught me something important about how epic boss battles should work: not just hit points and armor class and actions, but multiple environmental factors at once (searching for clues, collapsing cabins, burning books) that gives everyone a chance to risk it all while under immense pressure. Sometimes, heroics isn't just battling bags of hit points, but finding the right clue at the right time.
Your Turn: How do you run big group boss fights?
