Boss monsters are a hallmark of adventure design. In the climactic battle, the PCs end the boss’s schemes and save the day.
Especially at lower levels though, boss monsters can be dull. They can be guileless and lack interesting abilities beyond swinging a sword and commanding underlings to an early grave.
So how do we fix boss monsters? We rebuild them into dynamic stat blocks.
See previous Boss Fights articles here!
The Sausage Making
Building a dynamic boss battle involves several steps. To make your own, follow these steps:
1. Separate the monster’s attitude toward combat into three phases.
2. Break out the monster’s published stat block to match each phase.
3. Use or modify existing abilities that match the attitude for each phase. To improve boss effectiveness and survivability, add new reactions and bonus actions to make good use of the action economy.
4. Introduce lackeys with low hit points. Several full-blown allies can bog down combat, but lackeys (with a fraction of hit points that a standard monster of their type would have) provide an obstacle without slowing the tempo.
5. Add lair actions. A clever boss fights on their own terms. Even cornered, a boss monster chooses the battlefield, which grants them special actions on their turf.
Each article focuses on different aspects of these boss fights. This time focuses on modifying existing abilities that match the tone of the battle for each phase.
Treant
This article adapts the treant from the System Resource Document (SRD). Its “lair” is a lightly forested area where a group of human and elven settlers built a treetop village. These settlers failed to obtain permission from the forest, and the treant now comes to violently evict them. It won’t negotiate, intending to make an example of the village.
This places the PCs between a rock and a hard place—while the treant’s cause is perhaps noble, its methods will harm many innocents. Stopping the rampaging forest guardian will hopefully force negotiations (or allow for a peaceful evacuation).
The treant summons lackeys to reclaim its lair: vines of Nemthyr (see Creature Codex) and shambling mounds. The treant also relies on surrounding forest, including the oaks, birches, and hickories that cry out under the strain of their residential shackles.
Each boss phase represents the treant’s attempts to drive the settlers from its forest home: lumbering treant, ousting treant, and incensed treant.
While normally CR 9, this treant is CR 11 while retaking its lair. PCs who defeat the incensed treant receive 7,200 XP.
In the initial phase, the treant makes its presence known by shouting accusations while launching rocks at the village’s structures. The treant previously plotted its approach, strategically placing rocks at 15-foot intervals in the prior week.
It uses its Horrid Vines bonus action to create lackeys to intercept foes who seek to engage it in melee, even though it can slink out of combat with its Slow Trot.
Lumbering Treant (Phase 1)
Huge Plant, Usually Chaotic Good
Armor Class 16 (natural armor)
Hit Points 69 (6d12 + 30)
Speed 30 ft.
| STR | DEX | CON | INT | WIS | CHA |
| 23 (+6) | 8 (−1) | 21 (+5) | 12 (+1) | 16 (+3) | 12 (+1) |
Damage Resistances bludgeoning, piercing
Senses passive Perception 13
Languages Common, Druidic, Elvish, Sylvan
Challenge 9 (5,000 XP) Proficiency Bonus +4
Alchemical Treatment. The treant has been treated with unguents and oils to prevent forest fires. After taking 50 points of fire damage in a single day, the treatment fails and the treant becomes vulnerable to fire damage.
False Appearance. While the treant remains motionless, it is indistinguishable from a normal tree.
Siege Monster. The treant deals double damage to objects and structures.
ACTIONS
Multiattack. The treant makes two Slam attacks.
Slam. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 16 (3d6 + 6) bludgeoning damage.
Rock. Ranged Weapon Attack: +10 to hit, range 60/180 ft., one target. Hit: 28 (4d10 + 6) bludgeoning damage.
Boulder Volley (Recharge 4–6). Ranged Weapon Attack: +10 to hit, range 60/180 ft., three targets. Hit: 16 (3d6 + 6) bludgeoning damage.
BONUS ACTIONS
Horrid Vines (2/phase). The treant summons 1d4 + 1 lackeys (vines of Nemthyr with 10 hp) it can see within 60 feet of it. These lackeys act on initiative count 5.
Slow Trot. The treant moves 15 feet without provoking opportunity attacks.
LAIR ACTIONS
On initiative count 20 (losing initiative ties), the treant takes a lair action to cause one of the following effects:
- Hungering Green. Each enemy creature within 120 feet of the treant makes a DC 18 Strength saving throw. On a failure, it is pulled in a straight line 20 feet toward the treant or a lackey. On a success, it is pulled 10 feet.
- Vicious Undergrowth. Two target creatures within 120 feet of the treant make DC 18 Strength saving throws or become restrained until the end of their next turn.
- Village Debris. As the trees come alive, the village above starts to fall. Two target creatures within 120 feet of the treant make Dexterity saving throws at DC 18 or take 14 (4d6) bludgeoning damage or half damage on a successful save. Creatures that fail by 5 or more become grappled until the end of their next turn.
In this phase, the treant reaches the outskirts of the village and summons the full fury of the forest. It calls upon enslaved trees to throw the shackles from their branches, and it even sunders the ancient woodland floor to aid its cause. Shambling mounds crawl from the tree line to aid the treant’s cause.
Ousting Treant (Phase 2)
Huge Plant, Usually Chaotic Good
Armor Class 16 (natural armor)
Hit Points 69 (6d12 + 30)
Speed 30 ft.
| STR | DEX | CON | INT | WIS | CHA |
| 23 (+6) | 8 (−1) | 21 (+5) | 12 (+1) | 16 (+3) | 12 (+1) |
Damage Resistances bludgeoning, piercing
Senses passive Perception 13
Languages Common, Druidic, Elvish, Sylvan
Challenge 9 (5,000 XP) Proficiency Bonus +4
Alchemical Treatment. The treant has been treated with unguents and oils to prevent forest fires. After taking 50 points of fire damage in a single day, the treatment fails and the treant becomes vulnerable to fire damage.
False Appearance. While the treant remains motionless, it is indistinguishable from a normal tree.
Siege Monster. The treant deals double damage to objects and structures.
ACTIONS
Multiattack. The treant makes two slam attacks.
Slam. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 16 (3d6 + 6) bludgeoning damage.
Rock. Ranged Weapon Attack: +10 to hit, range 60/180 ft., one target. Hit: 28 (4d10 + 6) bludgeoning damage.
Branching Strike (Recharge 5–6). The treant makes a slam attack against each creature within a 15 ft. cone.
BONUS ACTIONS
Abundant Undergrowth (1/phase). The treant magically animates 1d4 + 1 lackeys (shambling mounds with 10 hp) it can see within 60 feet of it. These lackeys act on initiative count 10.
Strong Right Bough. The treant makes a slam attack.
LAIR ACTIONS
On initiative count 20 (losing initiative ties), the treant takes a lair action to cause one of the following effects:
- Overgrowth. The treant gains 18 (4d8) temporary hp. It and all of its lackeys gain +2 AC until the end of the treant’s next turn.
- Ruined Civilization. The old elven road upheaves in fury, and all enemy creatures must make DC 18 Strength saving throws. On a failure the creature takes 18 (4d8) thunder damage and falls prone, or half as much on a successful save. Creatures who fail their saves by 5 or more are pushed 20 feet in a random direction.
- The Forest Lives. The trees start to come alive and shake the homes from their roofs. The treant chooses a point at two locations it can see. Each creature in a 10 foot radius of that point makes a DC 18 Dexterity saving throw, taking 21 (6d6) bludgeoning damage or half as much on a success. Creatures who fail the save by 5 or more are stunned until the end of their next turn.
In the final phase, the treant becomes enraged at the resistance it encounters. It summons the most dangerous foliage from its lair, causing the most grievous harm to its foes. It also calls recently-freed trees to battle, whether as lackeys or mammoth clubs, and it may grasp villagers to use as bargaining chips following any flight from the fray.
Incensed Treant
Huge Plant, Usually Chaotic Good
Armor Class 16 (natural armor)
Hit Points 69 (6d12 + 30)
Speed 30 ft.
| STR | DEX | CON | INT | WIS | CHA |
| 23 (+6) | 8 (−1) | 21 (+5) | 12 (+1) | 16 (+3) | 12 (+1) |
Damage Resistances bludgeoning, piercing
Senses passive Perception 13
Languages Common, Druidic, Elvish, Sylvan
Challenge 9 (5,000 XP) Proficiency Bonus +4
Alchemical Treatment. The treant has been treated with unguents and oils to prevent forest fires. After taking 50 points of fire damage in a single day, the treatment fails and the treant becomes vulnerable to fire damage.
False Appearance. While the treant remains motionless, it is indistinguishable from a normal tree.
Siege Monster. The treant deals double damage to objects and structures.
ACTIONS
Multiattack. The treant makes two slam attacks.
Slam. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 16 (3d6 + 6) bludgeoning damage.
Rock. Ranged Weapon Attack: +10 to hit, range 60/180 ft., one target. Hit: 28 (4d10 + 6) bludgeoning damage.
Uproot (Recharge 5–6). The treant takes another tree, uproots it, and makes a slam attack against all creatures in a 20-foot line.
BONUS ACTIONS
Animate Trees (1/Phase). The treant magically animates 1d4 + 1 lackeys (treants with 10 hp without the Animate Trees bonus action) it can see within 60 feet of it. These lackeys act on initiative count 15.
Arresting Grasp. The treant grapples a Medium or smaller creature it hits with its slam attack (escape DC 18). The treant can’t grapple more than two creatures at one time, and it can’t use Multiattack or Uproot while grappling a creature.
LAIR ACTIONS
On initiative count 20 (losing initiative ties), the treant takes a lair action to cause one of the following effects:
- Arboreal Rage. Each enemy creature within 5 feet of the treant or treant lackey must make DC 18 Dexterity saves. On a failed save, the creature takes 10 (3d6 + 6) bludgeoning damage, or half as much damage on a successful one.
- Evergreen Typhlosis. Each enemy creature makes a DC 18 Wisdom saving throw or have disadvantage on Wisdom (Perception) checks that rely on vision for 10 minutes. Creatures who fail by 5 or more are blinded until the end of their next turn.
- Verdant Stream. A lackey that died in the last minute returns to life with 10 hp.
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About Benjamin Eastman
Benjamin L. Eastman was introduced to D&D by his four closest friends—who immediately betrayed his trust by sacrificing his first character to a demonic artifact. Undeterred, he’s played all manner of RPGs in the intervening years. In addition to writing Warlock Lairs and monsters for Kobold Press, he’s contributed to the Stargate RPG and Americana, and co-authored DMs Guild adventures including Baby Tarrasque. He is perhaps proudest of the bar brawl—his first published monster in the Creature Codex.
