Gargantuan undead, lawful neutral

Armor Class: 20 (natural armor)

Hit Points: 420 (24d20 + 156)

Speed: 0 ft

STR

25 +7

DEX

10 +0

CON

23 +6

INT

18 +4

WIS

16 +3

CHA

16 +3

Saving Throws: STR (+16), DEX (+4), CON (+15), INT (+12), WIS (+8), CHA (+10)

Skills: Insight (+10), Intimidation (+13), Perception (+17), Persuasion (+10)

Damage Vulnerabilities: Fire

Damage Resistances: Necrotic, Nonmagical Bludgeoning, Piercing, & Slashing

Damage Immunities: Poison

Condition Immunities: Charmed, Frightened, Grappled, Incapacitated, Paralyzed, Petrified, Poisoned, Prone, Restrained, Stunned

Senses:

• Blindsight. 120ft.
• Passive Perception: 22

Languages: All languages its victims knew

Challenge Rating: 24

Actions

• Multiattack. The Gravemind can use its Frightful Presence. It then makes three attacks; one Bite attack and two Slam attacks.
• Bite. Melee Weapon Attack: +16 to hit, reach 20ft., one target. Hit: 50 (8d8 + 10) piercing damage.
• Slam. Melee Weapon Attack: +16 to hit, reach 30ft., one target. Hit: 32 (6d6 + 8) bludgeoning damage.
• Frightful Presence. Each creature of the Graveminds choice that is within 120ft. of it and aware of it must succeed on a DC 20 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the save at the end of each of its subsequent turns, ending the effect on itself on a success. If a creature saves successfully or the effect ends for it, the creature is immune to this feature for 24hrs.
• Infectious Breath (Recharge 5-6). The Gravemind exhales a cloud of infectious Flood spores in a 120ft. cone. Each creature in that area must make a DC 26 Constitution saving throw or suffer the effects of the Flood Infection.

Legendary Actions

The Gravemind 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 Gravemind regains spent legendary actions at the start of its turn.

• Biomass Shell. The Gravemind channels nearby biomass to form a protective shell, granting itself 24 (4d6 + 8) temporary hitpoints.
• Focus Flood. The Gravemind selects one creature. The next attack against the chosen creature is made with advantage.
• Mucus. The Gravemind causes a layer of mucus to form over all surfaces within 60ft. of it that lasts for 1 round. Surfaces coated in the mucus are treated as difficult terrain.

Lair Actions

On initiative count 20 (losing initiative ties), the Gravemind takes a lair action to cause one of the following effects; the Gravemind can't use the same effect two rounds in a row.

• Summon Flood Crawlers. 8 Swarms of Flood Crawlers form from biomass in an unoccupied space within 60ft. of the Gravemind.
• Summon Flood Screechers. 4 Swarms of Flood Screechers form from biomass in an unoccupied space within 60ft. of the Gravemind.
• Summon Flood Stalkers. 8 Flood Stalkers form from biomass in an unoccupied space within 60ft. of the Gravemind.
• Summon Flood Combatants. 8 Flood Combatants form from biomass in an unoccupied space within 60ft. of the Gravemind.
• Summon Flood Carriers. 8 Flood Carriers form from biomass in an unoccupied space within 60ft. of the Gravemind.
• Summon Flood Dragon Wyrmling. 2 Flood Dragon Wyrmling forms from biomass in an unoccupied space within 60ft. of the Gravemind.
• Summon Young Flood Dragon. 1 Young Flood Dragon forms from biomass in an unoccupied space within 60ft. of the Gravemind

Regional Effects

The region contains The Gravemind's lair is corrupted by its mere existence, which creates one or more of the following effects:

• The land within 6 miles of the lair is littered with patches of rotting biomass. These patches count at difficult terrain and creatures that start their turn on one of these patches must succeed on a DC 10 Constitution saving throw or suffer the effects of the Flood Infection.
• Water sources within 1 mile of the lair are ripe with Flood spores. Creatures that drink it must succeed on a DC 13 Constitution saving throw or suffer the effects of the Flood Infection.
• Green fog lightly obscures the land within 6 miles of the lair. Bloodied creatures that enter this area for the first time must succeed on a DC 10 Consitution saving throw or suffer the effects of the Flood Infection.