The Elder Fungus and Blights

In the years before Strahd's conquest of the Valley, the druids that lived here were a small commune that were left to worship their strange god in peace. When he took over, the dark powers he consorted with twisted the land, and twisted the druids that were so in tune with it. The places where they placed their esteemed dead and performed their rituals became ghastly caricatures of what they had been before. While the druids were never benevolent, they went from slightly sinister nuisances to actively malevolent blights on the people of the Valley.
The Elder Fungus that gives the druids their power has been strongly empowered by the dark powers that have Barovia in their grasp. It is fed by the constant misery and the steady stream of bodies that Barovia now provides, and it is able to use its strength to bolster its druids, who are able to bring it yet more bodies, and spread its spores further through the forest. Eventually, it hopes to conquer all of the valley. This is not a powerhungry ambition, of course, it is a plant: its purpose is to spread and procreate, and Strahd has given it the perfect place to do so.
The Elder Fungus replaces the Gulthias tree. Corpse blights replace needle blights. Root blights replaces vine blights. Shroom blights replace twig blights.

Homebrew

Elder Fungus CR: 4

Huge plant, neutral

Armor Class: 15

Hit Points: 76 (8d10 +40) 8d10+40

Speed: 0 ft

STR

20 +5

DEX

1 -5

CON

18 +4

INT

1 -5

WIS

11 +0

CHA

18 +4

Saving Throws: Constitution +9

Damage Vulnerabilities: Fire

Damage Resistances: Psychic

Damage Immunities: Necrotic, Poison

Condition Immunities: Blinded, Charmed, Deafened, Exhaustion, Frightened, Poisoned, Prone

Senses: Tremorsense 60 ft., Passive Perception 10

Languages: None

Challenge Rating: 4

Rooted. The Elder Fungus is immune to any effect that would move it.
Spore Thralls. If a humanoid spends a full 24 hours within 10ft of the Elder Fungus, it falls into a deep slumber. The creature then must succeed on a series of three Constitution saving throws, with increasing DC's of 10, 15, and 18. If the creature succeeds all three saving throws, it rises as a thrall of the Elder Fungus. The thrall exists only to serve and defend the Elder Fungus. It possesses all of its former abilities, and gains the Halo of Spores ability. If the creature fails any of its Constitution saving throws, it dies and is absorbed by the Fungus. For every creature the Fungus absorbs in this way, it gains +5 to its maximum HP.

Actions

Create Blights (Recharge 6). When threatened, the Elder Fungus can defend itself by creating spore blights. It releases a low piercing shriek, and the blights erupt from the ground and act immediately. Roll 1d8, 1d6, and 1d4 for the number of shroom, root, and corpse blights respectively.

Reactions

Spore Release. When the Elder Fungus, it can use its reaction to release a cloud of thick spores. All creatures within 5 ft. of the Fungus must succeed a DC 14 Constitution saving throw or become poisoned as the spores burrow into their flesh. While poisoned in this way, a creature suffers disadvantage on all attack rolls, saving throws, and ability checks. Creatures may make another Constitution saving throw (DC 13) at the end of their turn to end this effect. Anyone who fails the saving throw is covered with small mushrooms. These mushroom wither upon taking a short rest or when subjected to any form of magical healing.

Legendary Actions

The Elder Fungus can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. The Elder Fungus regains spent legendary actions at the start of his turn.
Bolster Thralls (Costs 3 Actions). The Elder Fungus targets all spore blights and creatures with the Spore Thrall trait within 30 feet. If a target can see the Elder Fungus, it regains 1d4 + 4 hit points.
Create Blights (Costs 2 Actions). The Elder Fungus releases a low piercing shriek. Roll a d6. If it is a 6, the Elder Fungus uses its Create Blights ability, even if it has not recharged yet.
Defend Me! The Elder Fungus targets one ally within 30 feet of it. If the target can see the Elder Fungus, the target can make one weapon attack as a reaction and gains advantage on the attack roll.

This massive fungal colony is the source of the Barovian druids' power. It resembles both a mushroom and a tree, with a massive cap that resembles a thick canopy of grasping fingers. Its base is a creeping tangle of similar tendrils that burrow into the ground. The soil around is green and sickly, and nothing grows for 100 ft of the Fungus.

Lesser Fungus CR: 7

Huge plant, any

Armor Class: 15 (natural armor)

Hit Points: 149 (13d12 + 65) 13d12+65

Speed: 30 ft

STR

23 +6

DEX

10 +0

CON

20 +5

INT

6 -2

WIS

10 +0

CHA

3 -4

Damage Resistances: psychic

Damage Immunities: Necrotic, Poison

Condition Immunities: blinded, deafened

Senses: blindsight 60 ft. (blind beyond this radius), passive Perception 10

Languages: Understands Common and Druidic, but cannot speak

Challenge Rating: 7

Siege Monster. The blight deals double damage to objects and structures.

Actions

Multiattack. The blight makes four attacks: two with its tendrils and two with its grasping roots. If it has a target grappled, the blight can also make a bite attack against that target as a bonus action.
Bite. Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 19 (3d8 + 6) [roll3d8+6] piercing damage and 8 (2d4 + 4) [roll2d4+4] poison damage.
Tendril. Melee Weapon Attack: +9 to hit, reach 15 ft., one target. Hit: 16 (3d6 +6) [roll3d6+6] bludgeoning damage.
Grasping Root. Melee Weapon Attack: +9 to hit, reach 15 ft., one creature not grappled by the blight. Hit: the target is grappled (escape DC15). Until the grapple ends, the target takes 9 (1d6 +6) poison damage at the start of each of its turns as the roots inject them with spores. The root has AC15 and can be severed by dealing 6 slashing damage or more at it at once. Cutting the root doesn't hurt the blight, but does end the grapple.

Shroom Blight CR: 1/8

Small plant, neutral

Armor Class: 13 (natural armor)

Hit Points: 4 (1d6 +1) 1d6+1

Speed: 20 ft

STR

6 -2

DEX

13 +1

CON

12 +1

INT

4 -3

WIS

8 -1

CHA

3 -4

Skills: Stealth +3

Damage Vulnerabilities: Fire

Damage Resistances: Necrotic, Poison

Condition Immunities: Blinded, Deafened, Exhaustion, Poisoned

Senses: Blindsight 60ft. (blind beyond this radius), passive Perception 9

Languages: None

Challenge Rating: 1/8

Actions

Bite. Melee Weapon Attack. +3 to hit, reach 5ft., one target. Hit: 3 (1d4 + 1) acid damage.

These blights resemble small humanoid mushrooms. Their bodies are smooth, and their skin is sticky and soft. They have no faces, but closer inspection reveals they have huge soft mouths full of acidic saliva.

Corpse Blight CR: 1/2

Medium plant, neutral

Armor Class: 12 (natural armor)

Hit Points: 26 (4d8 + 8) 4d8+8

Speed: 20 ft

STR

15 +2

DEX

8 -1

CON

14 +2

INT

5 -3

WIS

10 +0

CHA

3 -4

Skills: Stealth +2

Damage Vulnerabilities: Fire

Damage Resistances: Necrotic, Poison

Condition Immunities: Blinded, Deafened, Exhaustion, Poisoned

Senses: Blindsight 60 ft. (blind beyond this radius), passive Perception 10

Languages: None

Challenge Rating: 1/2

False Appearance. While the blight remains motionless, it is indistinguishable from a corpse.

Actions

Grapple. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 9 (2d6+2) bludgeoning damage, and a Large or smaller target is grappled (escape DC12). Until the grapple ends, the target is restrained , and the blight can't grapple another target.
Exhale (Recharge 5-6). The blight exhales hard, releasing a small cloud of spores from the rotting holes in its body. All creatures that end their turn within a 10 ft. radius of the blight must succeed a DC12 Constitution saving throw or take 1d6 of poison damage.

These medium-sized blights are the most horrific of the Elder Fungus's creatures. They are the corpses of those the Fungus has absorbed, reanimated with the spores and mushrooms of the Elder controlling the rotting flesh. These corpses appear ordinary at first glance, but once they rise, they begin to softly glow, and you can see the spores growing from their rotting flesh.

Root Blight CR: 1

Medium plant, neutral

Armor Class: 12 (natural armor)

Hit Points: 11 (2d8 + 2) 2d8+2

Speed: 30 ft , climb: 20 ft

STR

12 +1

DEX

12 +1

CON

13 +1

INT

4 -3

WIS

8 -1

CHA

3 -4

Damage Resistances: Fire

Condition Immunities: Blinded, Deafened, Exhaustion, Poisoned

Senses: Blindsight 60 ft. (blind beyond this radius), passive Perception 9

Languages: None

Challenge Rating: 1

Enflame. Unlike its fellow blights, the Root Blight is not vulnerable to fire. Attempts to set it ablaze instead strengthen it. If the Blight takes fire damage, it immediately becomes Enflamed, and all its attack do an additional 1d4 of fire damage.

Actions

Multiattack. The root blight makes two claw attacks.
Claw. Melee Weapon Attack. +3 to hit, reach 5 ft., one target. Hit: 6 (2d4 + 1) piercing damage.
Rotting Touch. (Recharge 5-6) Melee Weapon Attack. +3 to hit, reach 10 ft., one target. Hit: 8 (1d8 + 4) necrotic damage.

These blights are an amalgamation of the roots of plants and trees the Elder Fungus has infected. They gather in a vaguely humanoid shape, which rustles and whistles unsettlingly as it moves.

SRD, Homebrew

Barovian Druid CR: 2

Medium humanoid, any evil

Armor Class: 11

Hit Points: 27 (5d8 +5) 5d8+5

Speed: 30 ft

STR

10 +0

DEX

12 +1

CON

13 +1

INT

12 +1

WIS

16 +3

CHA

11 +0

Skills: Medicine +4, Nature +3, Perception +4

Senses: Passive Perception 14

Languages: Druidic

Challenge Rating: 2

Spellcasting. The Barovian druid is a 5th-level spellcasters. Its spellcasting ability is Wisdom (spell save DC14, +4 to hit with spell attacks).
Cantrips (at will): druidcraft, chill touch, shillelagh
1st level (4 slots): fog cloud, entangle, longstrider, faerie fire
2nd level (3 slots): barksin, protection from poison
3rd level (2 slots): gaseous form, plant growth

Actions

Quarterstaff. Melee Weapon Attack: +2 to hit (+4 to hit with shillelagh), reach 5 ft., one target. Hit: 3 (1d6) bludgeoning damage, 4 (1d8) bludgeoning damage if wielded with two hands, or 6 (1d8 + 2) bludgeoning damage with shillelagh.

Reactions

Halo of Spores. As a reaction, the druid can activate the "Halo of Spores" ability available to Circle of Spore druids. This allows them to use their reaction to deal 1d4 necrotic damage to any creature that moves through or starts its turn within 10 feet of them. The affected creature must succeed a Constitution save against the druid's spell save DC to avoid taking the damage.

The druids in Barovia existed before Strahd, and while they now serve him, they do not worship him. They worship neither the powers he consorts with, nor the powers that existed in Barovia before him. They instead worship the land itself, and a fabricated god of their own that venerates the rot and decay after death. They wish to spread this decay through the land, as they see the stagnance that Strahd has brought as unnatural and depraved.